I am currently using an Arrma 17T pinion, but also not using the stock motor. Running a Tenshock motor. I haven't had any issues with the Arrma gear.
As far as adjustment, I just pull the 5 screws out from the bottom and pull the whole assembly out. Easier than hunting for my Allen's that came with the truck. Lol.
winner winner.
Also, don't forget that the three screws into the motor mount (under the chassis) are thread locked, heat them before trying to torque them off.