I'd say don't do it, but I'm one of the highly critical perfectionist types. If I'm not challenged, I don't try. It depends on if you can grow while you study there - if you don't see that, I wouldn't. Relationships with faculty are important, and if they perceive you're not into it, they won't put their efforts into you. It seems they want you, they're giving you a good deal, and if you take off it might be wasted effort.