Performance

The c-Jays main force is that you can alter the sound a bit by swapping the pads. The thinnest of the sets provides you with the biggest bass, but also the smallest sound stage. Those thin pads also have the worst wearing comfort of all the pads because they do not dissipate the clamping force of the headband that well.
Moving up to the medium sized ones you get a really good wearing comfort and still retain a good bass performance, considering it is a light weight set of portable headphones. The variation in sound stage width and depth is basically non existing between the thinnest and the medium sized pads. Before I began my listening sessions, the headphones had about 120 hours on them so their performance should not change that much beyond that point.
Sound signature wise they are a bit on the cold side with a quite aggressive sound sort of like Yuin OK1s, however, not as extreme. The bass is where it needs to be for the majority of music types with the two smallest sets of pads. With the huge bowls on, the bass gets pushed back in the mix to an extent were it damages the sound balance.

The signature is a bit cold, but not overly analytical. They have a quite good midrange and bass with the right pads on. What they lack is sound stage, but portable headphones with a good sound stage are a rarity. Timbre wise they are a alright, but the note decay is to fast in order to be believable. The whole customizable aspect of the sound signature is something that is fun to play with, it does not alter the listening experience that much, but as a way to "tweak" the sound it does an alright job. Do not expect a night and day difference in the sound signature between the using the flat pads or the big bowls.

Treble and bass extension is quite good for a set of open back headphones, especially when taking into account that these are made for portable use.

What I like about the c-Jays is that they are incredibly light and much tougher than they look. Being supra-aural headphones with a medium amount of pressure exerted by the headband they are quite comfortable to use on the move. They do leak quite a bit of sound though so they are not ideal for listening to obscure tones on the bus. Another noteworthy aspect of their performance is that they can be driven by a normal DAP, no need for lugging around an expensive headphone amplifier. The gain in sound quality between running these from my DAP or one of the headphone amplifiers I currently own is slim, and on the move in a noisy environment I would never be able to tell the difference.

The c-Jays are worthy of consideration if you are looking for a set of balanced sounding supra-aural headphones and value mobility high. Compared to a set of Grado SR-60 the c-Jays offer a slightly more balanced sound with a wee bit less bass, and less sparkle. The only aspect where the Jays headphones pull ahead is in terms of wearing comfort, and practicality. The c-Jays also leak less sound than their Grado equivalent which is nice.

Compared to a set of clip-ons like the Yuin G1s the c-Jays have a leaner sound and are not quite as resolving. The two headphones cost the same $129, but the G1s crave a headphone amplifier to show their true self. Extension wise the c-Jays hold their own against the closest competitors, they are a bit brighter than the G1s and not quite a spikey in the upper mids as the Grados.

Durability

Even though the Jays c-Jays have a very slim design they are still durable enough to be used on a daily basis. The headband construction seems solid enough and so does the ear cup and driver suspension mechanism.