I don't own one, but I've looked them over pretty close. I've owned a fair number of KSC/KWA Glocks over the years, and still own several.
The brunt of it in my experience is that basically it's a KWA Glock same as always in a different shaped skin. I'm not positive but I suspect you could swap slides, I know you can swap mags between them and the old system since I've done it. But overall I think it's safe to assume that you can read the old reviews of KWA glocks and get a good impression on the system as a whole.
GBB's and I have a love/hate relationship, and it leans towards hate more often than not. As such I don't really use them often and our weather doesn't help. But out of the GBB's I own and brands I own which is 10+ right now. I like the KWA slightly just slightly better than the others I've got. About the only major GBB company from the old days I don't have on hand is a TM. I've got good solid TM clone guns from companies that haven't existed though in 10+ years. And I'd say I still just slightly like the KSC/KWA better. The only GBB I'd say I liked even more than them is the WA guns I've run over the years, but allot of guys didn't care for them either.
So if you can get over the styling I think they are probably a good choice.
Luke