I've fired one on many occasions and they work fine. However, many owners feel that Bushmaster didn't continue to develop on the design and improve it. Function wise no real problems. Most complaints / observations for improvement are, bad top mount surface/rail area, it can be worked with other accessories, but it's not as easy to work with as a flat top AR. Magazine changes take practice because they're not in the standard AR location. Short sight picture. Again all of these things can be dealt with by either practice or accessories.
The largest problem now is that Bushmaster is discontinuing production.