If you've got a Colt and it's shooting good groups, there's absolutely nothing wrong with them. Buying a Colt off-the-shelf M4 wouldn't be something I'd recommend to anyone, simply because their accuracy is hit-and-miss, in my experience.
I don't think anyone here is going to bash them on quality, other than you can (usually) get a more accurate rifle, that works just as well, cheaper.
Sounds to me like you're in good shape. 
