While you can live with the extra room behind the toilet, the inspector may not allow the installation of the toilet without the required minimum 15" side-to-side. The Uni-fit adapter probably wouldn't allow that much slop. You might get some of that, but not all (I don't think). I've only dealt with a couple in my own home, so I'm not sure.
Were the walls up when the plumber installed the flange? If so, he should move it as it isn't code compliant (IMHO). If you installed the walls after, then it's your problem.
My personal take on offset flanges is avoid them.