Ever since their first Ultralight release back in 2018, Finalmouse have been all about getting mouse weight as low as possible. To this end, Finalmouse has been turning towards more exotic materials, starting with the magnesium-made Starlight in 2021. For the UltralightX, Finalmouse utilizes a carbon fiber composite, which appears to combine carbon fiber with other materials such as polycarbonate or epoxy resin to various degrees. While the magnesium shell of the Starlight was easily identifiable as a metal due to its stiffness, the material used for the UltralightX is more reminiscent of common ABS plastic, with its elasticity varying across the shell.

In addition to the exotic material, the UltralightX pulls the usual methods of lowering the weight where possible: Hexagonal holes are virtually everywhere except for the upper portion of the main buttons, there is no CPI button, no RGB lighting, no button cover for the on/off-switch, and even screws have been done away with, in favor of copious amounts of hot glue. The result of these efforts is a weight of 38 g for the medium size ("Lion"), which no doubt is impressive. At the same time, it effectively is no different from the similarly sized G-Wolves HTX 4K (honeycomb variant), which managed to achieve a weight of 39 g using plain ABS plastic, and a year earlier than the UltralightX no less. Whereas the HTX 4K is surprisingly solidly built, mostly owing to its design where the PCB has been extended such that it aids with structural rigidity, the UltralightX doesn't fare quite as well. On my sample, which is from the second batch, some parts are quite solid, while others are less so. More specifically, there is no rattle when shaking the mouse, and when applying force directly under the side buttons, the sides creak a bit but don't flex much, but when doing the same specifically at the intersection between the main buttons and sides, plenty of flex is present there. A particularly bad spot is the top, as when pressing there, the entire top effectively contracts. Thankfully, actuating the side buttons at least is impossible regardless of the force used. Another weak spot are the main buttons, which tend to give a crunchy sensation when pressing towards the edges, especially the outer ones. Either way, the overall impression is not a solid one, and even if we assume that these things improve as the production process matures over time, I struggle to see how this material could be considered unequivocally superior to common ABS plastic.

Since the rather stiff main buttons of the Starlight weren't received too positively, Finalmouse made a particular effort to ensure that the main buttons are light and easy to spam on the UltralightX. For this reason, Finalmouse went back to the trusty old Omron D2FC-F-7N (20 M) (OF) switches, which still are among the more balanced mechanical switches available, providing tactile actuation without being overly stiff. The button design, on the other hand, leaves something to be desired, as pre-travel is moderate and post-travel high, resulting in a button response that isn't as snappy as it could be. In addition, the buttons can be moved a decent bit laterally, though this only becomes noticeable when explicitly provoked, but not in-game. For the side buttons, a pair of surface-mounted switches likewise from Omron see use, which both score with low post-travel, and even though pre-travel is a bit higher on the back button, the actuation point remains even regardless, and button response is snappy and pleasing. The scroll wheel encoder comes from Kailh, and while noise levels are high, tactility is good, as the steps are rather nicely separated, allowing for controlled scrolling. Previous Finalmouse scroll wheels were known to eventually start to malfunction, in that physically scrolling up instead resulted in scrolling down, and vice versa. Whether this applies to the UltralightX at some point remains to be seen, but from what I've been able to gather, this behavior appears improved at least. Lastly, the feet are the usual pure PTFE fare and glide well. The biggest novelty in this regard is the fact that much like on the G-Wolves HTX or Hati-S Plus, the base is level, allowing one to use feet of most shapes or sizes in lieu of the default ones.

The most significant improvement the UltralightX brings over its predecessors doesn't so much lie in its physical makeup but rather in the firmware, along with the resulting performance uplift. Unlike the Starlight, which was restricted to USB full-speed, the UltralightX with its wireless dongle is a USB high-speed device, and thus natively capable of polling rates above 1000 Hz. Though 8000 Hz had been advertised for launch, only 2000 and 4000 Hz are available still at this time. In practice, this matters little, as performance is excellent regardless of polling rate. At 1000 Hz, the UltralightX already enjoys a lead of more than 0.5 ms in terms of motion delay over the Logitech G403, and this gap only widens to more than 1 ms at 4000 Hz. This of course only applies with MotionSync disabled, as upon enabling MotionSync, various amounts of motion delay are added, which is why keeping it off is recommended. For click latency, polling rate has less of an effect, and somewhat counterintuitively, lower polling rates result in lower click latency. This is due to the UltralightX fully making use of the available microframes by sending click data ahead of motion data packets where possible, and at lower polling rates, there are more opportunities to do so due to there being fewer motion data packets to begin with. In any case, the UltralightX averages a mere 0.4 ms at 1000 Hz, edging out even Razer's numbers at 8000 Hz wireless, and at 4000 Hz, only marginally worse 0.5 ms can be measured. From what I can tell, polling is stable throughout as well, the odd off-period polls here and bout of elevated noise there notwithstanding. The only flaw with performance is CPI deviation, which is a bit larger than I'd want it to be at +5%, and since the UltralightX doesn't allow setting custom CPI steps by default, there isn't much one can do except for a solution explored further down in the next paragraph.

Speaking of adjustment, Finalmouse has come up with a novel way of doing settings on the UltralightX. Instead of an application that requires installing first, the dongle of the UltralightX connects through a website hosted by Finalmouse called XPanel, which then allows doing basic adjustments such as CPI (preset steps only), polling rate, and MotionSync, and even a battery life indicator is found there. For XPanel, WebHID is used, which is why only Chrome, Edge, and Opera are supported as of now. Thankfully, Finalmouse has released a desktop version of XPanel as well by now, so beyond the initial download, there is no need to use any of these browsers ever again. While the prospect of only having to open a website instead of being required to install a software is certainly appealing, functionally this is no different from the stand-alone application G-Wolves has for many of their mice, which doesn't require installation either, but does provide much more options than the rather barebones XPanel. As mentioned earlier, the restriction to fixed CPI steps in particular is annoying due to the degree of CPI deviation present, but luckily, modifying XPanel in this regard is quite easily done, as described here.

Finalmouse advertises "two months" of battery life for the UltralightX, which is among the most non-descriptive descriptions imaginable, as without specifying usage per day, this claim is essentially meaningless. Since the percentage-based battery life indicator is largely accurate and reliable, I'm able to give an at least rough estimation of expected battery life. At 4000 Hz, the indicator went down by 10% for every two hours of use. Hence, assuming linear consumption, roughly 20 hours can be expected, which would translate to a bit more than 80 hours at 1000 Hz. These numbers are roughly on par with the Razer Viper V2 Pro or Logitech G Pro X Superlight 2, though both use optical switches and slightly larger-capacity batteries, so the comparison isn't entirely apples-to-apples. Unfortunately, the charging process itself is plain miserable on the UltralightX. Since the battery has been optimized for capacity (lower C rating), charging is woefully slow at around 0.131 A, and due to how incredibly stiff the charging cable is, one feels every minute spent with the cable plugged in. Since XPanel exclusively connects to the dongle, not even settings can be changed in XPanel, so aside from twiddling one's thumbs and waiting it out, there isn't much one can do while charging, as gaming at least is off the table.

While previous Finalmouse releases were only sold once during dedicated "drops," which usually lasted the better part of five minutes, this has changed slightly at least with the UltralightX. The UltralightX is supposed to remain in continuous production, though it still is released through dedicated "drops," and therefore not continuously available, lest one seeks out aftermarket sellers, which typically come with ludicrous markups. If bought directly from Finalmouse, the UltralightX costs a whopping $189.00, albeit duty-free worldwide shipping is included with this at least. Effectively, the UltralightX therefore doesn't cost much more than the G-Wolves HTX 4K at $169.00, though that one at least can be bought at any time, and not just from G-Wolves, either. In any case, and regardless of the effort put into its engineering, the UltralightX is very pricey, to where I'm not sure if its quality is high enough to justify that cost. In particular, the build-related issues are more than just a nuisance, and for $189.00, I'd expect more than a charging cable whose stiffness gives Corsair's old cables a run for their money. For those who seek the absolute peak in terms of performance and weight without caring about anything else, the UltralightX is certainly worth a look, but the rest may be better off with more reasonably priced options. Still, the engineering effort put into the UltralightX is commendable, and warrants our Innovation award.