I've got one running right now. Everything in it was quite decent. I swapped out the stock piston for my own reason (it's kind of a silly build).
Shimming was pretty decent, parts/fit/function looked ok. I overheated everything (
) and one of the wires needed resoldering.
Personally...I'd buy another (and was about to if this build blew through these gears...which it did to 3 other gear sets...but it hasn't done anything to this KA mechbox so far).