I'll start by saying that this isn't from firsthand experience, this is from a friend who has one.
On the plus side, it's fairly gas efficient, at least on semi, it's also pretty light weight and both the pistol grip and foregrip feel solid enough. It wasn't used that much but it still worked last time I saw it.
However, his one did have a tendency to leak slightly, and outside of the pistol grip and foregrip, it did feel pretty cheap and the sights were crap, they didn't line up properly and the rear sight was loose.
Other then that, the hop up is fixed, internals are mostly metal and I can't really vouch for the accuracy outside of CQB.
Hope this helps a bit.