I have a "TSD" M4A1 FMU that was purchased from buyairsoft.ca and I have to say it's holding up quite well. Absolutely no barrel wobble, and the motor seems to be quite good.
The range i got in my last game with it was decent, although every 5th or 6th BB would slice off to the left after about 100-125ft. Not sure exactly what's causing it, but it doesn't happen all that frequently to get me really annoyed.
For the price I paid for a full metal M4A1 with upgraded internals, the performance is exceptional.
SRC Colt M4A1 FMU + CA Military M203 Long | TM G3 SAS | TM G3A3 | KJW Beretta M9 FMU
Ottawa Valley Airsoft