They're very unique - I quite like mine. I have three grips though (and they're big ones):
It leaks - the stock reservoirs leak, the internals leak at times. It really can be a bit of a bitch at times
The loading arms are terrible and will break at some point (upgrading to the Wiitech ones isn't too much money though)
It feels a bit flimsy and does bend a little after time. It's all plastic, so this can be expected but I get the feeling like if I fell on it it would just break in two immediately
All in all they're quite unique and certainly novel for CQB. It doesn't feel like cheap plastic though, that's for sure - the receiver is full metal for one. Skirmish-wise it's much more competitive then a springer - 3/6 shot modes, decent Marui hop (though fixed), quicker and easier operation than a springer.
Buy some re-enforced reservoirs or HPA tap it though.