[ceazer]

i happen to own both the ka m4 and a kwa km4 ris both guns perform awesome for me right out of the box. for the thread sake i will compare the kwa km4 (same internals-different externals)
king arms colt m4
pros:
functional boltcatch
100$ cheaper
tm compatible

kwa km4 2gx

2gx gearbox
9mm bearings
tb barrel 6.05-6.03 (says kwa)
faster rate of fire
lipo ready (says kwa)
2gx hop up
pretty much everything internally
externals (only based on colour) same build

both guns perform very well out of the box and the only thing both need to play would be a spring change (maybe not anymore 366+fps) but in my opinion if your looking for a start off gun platform for rebuilding and tinkering by all means go with the ka save 100$ but spend much more in parts and labour if you dont know what your doing, as for the kwa it comes stock not needing any major upgrades, so your decision should be based on what your planing on doing with your gun and go from there.
As for proprietary parts you shouldnt beleive the hype tm compatibility is not what it used to b.e these days with all the parts and different variety of retailers nothing is impossible and shouldnt sway the decisions of new gun buyers...
just my opinion!