Pro studios use Monitor Ones? As fucking if. Please name some such studios and explain the extent of their use (as opposed to just having them sit in a corner). Shit. Just name some pro studios that even own Monitor Ones. That way I can steer musicians away from studios that obviously do not invest in decent equipment.
As Igor mentioned, they may be adequate for beginners. However, the Monitor Ones are too forgiving, which can make it difficult to make a good mix that translates well to other systems. Yes, users do not mix as bass heavy, but they can tend to not notice overbearing trebel.
I strongly suggest staying away from the Monitor Ones. There are better options for the beginner, like the 20/20's. Check the archives for threads on best monitors.