I've heard nothing other than a few reviews on US Forums and one or two on YouTube, I made a topic about it on here a while ago, got no replies.
From what I've seen, they've all been good reviews though. Search YouTube and Google for them.
I've not seen the gun(s) in stock anywhere in the UK recently though, only on a few overseas websites, so you'll most likely have to order from there.
As for G&P as a company, from my experience with them (my M16 and my brother's M4), they've been very, very good. Amazing external and internal quality. I do get better results from a MadBull tight bore and a MadBull hop rubber over the stock G&P ones, but that's really to be expected from most guns out of the box.