However, there is a significant drop in FPS when fitted with the steel slide, as sown in their own video :
RA-TECH KSC MK23 STEEL SLIDE & WE AK74U WOOD KIT - YouTube.
I know you don't need massive amounts of FPS on a pistol, but going from 350ish to sub 290 sure is a lot. In 3 shots : 274, 285 and 264. 20 fps in variation.
The kick on it looks insane though.