A descent, fully built gearbox for the price. However, it required some work to get going right, hopefully your's does not.
Read Pro's and Con's for more info.
Fits most guns, although the Classic Army M15A4 is not an exception.
I put this gearbox into my Tokyo Maui G3 SAS after some mod's (see cons).
Swapped the spring to a M110, (this was due to not being able to fit the M120 spring back into place after it pop'd out from me swapping the trigger assembly) paired with a high speed G&G Motor and 9.6V Mini battery, the results have been more than satisfactorily for a cqb build.
The rate of fire is very high with the M110 spring, G&G motor and 9.6v battery installed.
The build of the gearbox seems it will hold for a long time.
(KEEP IN MIND) I had to also swap the selector panel and trigger to make it fit right in my TM G3 SAS, the trigger swap requires opening the gearbox, in which, the spring could shoot out, and I have never had such a hard time with a M120 spring going back into a gearbox quite like this, as it happened to me.
I couldn't get the gearbox to fit right in a Classic Army M15A4 Rifle.
After a few hours of messing around, I found that the M15A4 cannot take reinforced gearbox's due to the wider design of the gearbox, even after taking a Dremel to the metal body of my M15A4 for many hours.
Now, mine came without the contact wires from the trigger assembly to the selector panel, so I was forced to swap my old trigger assembly from my last gearbox into this one, hopefully, your's is not missing this also.
End thoughts about the product:
Although i'm disappointed about having to mod a few things, and the fact that it didn't fit right in my CA M14A4, it is still a good buy for what it is and i'd still recommend it to anyone who doesn't have the extra money to put down a Systema gearbox.