Nitro has its share of critics. But, there are satisfied customers as well. I get the impression that dealing with them on issues can be problematic if you use phone or email; but people who use their support forum (or PM their forum moderator) seem to be able to get what they need.

My brother had a World Models Sky Raider Mach I and it seemed pretty well built. The covering was not great though. He ironed all of the seams before assembly and the the covering still started lifting at the leading edge after a few flights. If I had not crashed it I think it would have needed a full covering job after a few months.