I own a KSC USP 45 Tactical System 7 with Metal slide, been shooting that baby for almost a year; about 3000 rounds.
Here are some observations:
The smallest portion of the slide guide may break if not properly lubed (due to slide cycling)
Front Sight is too loose: If not properly secured you may lose it while on the field.
As far as performance goes...
It has to be the best USP GBB.