"As this is the gearbox that comes stock with the newer APS v3 AEGs like their AKs and the UAR, I've had a chance to tinker with it (this is in my ASK209).
A quick aside on the internals, again assuming this is what they drop in their AEGs, internals are good. Mine was shimmed, had good aoe, and nice silver-plated wiring that's not soldered on. The grease was disgusting, but that's pretty much to be expected.
Now the real review, because if you're getting this it's probably to drop in something other than an APS AK. I tried dropping this into my other AKs and the verdict is...frustrated. Because this is a solid piece of work that makes spring changes and even regular gearbox assembly so much easier that is fatally crippled by a completely needless design flaw. This acutely applies to AKs, so there may not be an issue with other v3 guns.
The gearbox is designed to work with APS's blowback system, which on something like an AK, consists of a piece of metal that attaches to the charging handle and slides into the back of the gearbox like a dust cover button. This screws up the entire rear layout of the gearbox, because the slit where a typical AK dust cover button goes is now used for said EBB metal thing, and only that, because the slit is not backstopped, so a dust cover button can just slide out the back (assuming you find one that even fits, more below). In their AKs, APS uses a completely different button that fits onto a separate slit just above the normal slit. Not only does the placement of this slit makes it impossible for a normal button to properly fit in a dust cover, but I have yet to find any AK dust cover buttons that can even fit into the slits (tried a Marui, an E&L and 2 Cymas), as they appear to be more narrow. The only option, then, would be to use APS's own dust cover button that does work fine with and without the EBB, but APS neither sells nor includes in any gearbox packages, so the only place to find it is attached to an ASK which negates getting a separate gearbox in first place except as a replacement (unlikely because, as said before, this is pretty sturdy).
In a nutshell, if you're looking to get this for a standard AK, forget it. Until APS starts selling dust cover buttons, or better yet, starts producing these in a true standard form factor without the EBB nonsense, no quick-change for you.