The Angelbird Wings PX1 is a nifty little adapter that makes life just so much better for users of M.2 SSDs. First, it enables the full potential of high-performance M.2 SSDs to unfold when used on motherboards that don't have the Z170 or X99 chipset yet. Most Z97 motherboards, for example, only come with PCIe x2 2.0 bandwidth on their M.2 slot, which results in transfer rates of around 1 GB/s at most even though modern SSDs like the Samsung 950 Pro can go well into the 2.5 GB/s territory.
Angelbird's adapter is installed into a PCI-Express x4 slot (which obviously means it can also fit into an x16 "graphics card" slot), routing these four lanes to the PCIe SSD. If you have an older motherboard (Z97 or earlier), you should put it into a PCIe slot wired directly to the CPU to get PCIe Gen3 speeds, which makes sure data isn't sent via the chipset. This does, however, mean that your graphics card will be running at x8 3.0 instead of x16 3.0. We tested this in the past and the performance difference is negligible (0-1 % GPU performance). Such a setup will net you Gen3 PCI-Express x4 speeds, which will result in a maximum bandwidth of around 4 GB/s - plenty for even today's fastest SSDs.
We did some testing with the Samsung 950 Pro to look into what to expect from such an upgrade and found that real-life performance improved by 11% in our testing. Every single test saw noteworthy improvements with the exception of Battlefield 4 level loading, which I suspect is due to the PCIe SSD using up the bandwidth usually allocated to the graphics card for its ability to receive textures and models as a level loads.

The second improvement is for high-end M.2 SSDs, like the Samsung 950 Pro, under demanding workloads. These drives come with adaptive thermal throttling, which basically means that operating speeds are reduced as soon as the drive reaches a certain temperature to keep temperatures at safe levels. We also tested this and saw massive temperature improvements with the PX1 adapter's full-metal cover attached.

The only drawback of the PX1 is in my opinion its high price - at around US$75, it's much more expensive than competing adapters that are well below $20 but come without a heatsink. Most workloads will not require special cooling of the M.2 SSDs, so you are better off saving that money or spending it on a better SSD if you are right on budget unless you are hunting for the absolute highest performance in all situations. Other than pricing, there really isn't anything wrong with the Angelbird Wings PX1 adapter: it's of high-quality, easy to install, works without drivers, and delivers on all its promises.