I do know one thing. He's better than Pierre Woods, who also went to Michigan.
I'm a Michigan grad (like RIC and CS)... and I happen to like Crable.
There are some similarities to Woods, in that both were VERY highly recruited coming out of high school. It could also be argued, like a lot of other Carr-era players, that they didn't receive the coaching that maximized their strengths... but the flip side of the argument for both is that Woods and Crable didn't take advantage of their talents, either.
Pats, going back to Parcells, have always been interested in Michigan players due to pro-style system and traditional talent base. Once here, the Pats usually have had success "coaching them up". Brady, Law, Robert Perryman, Corwin Brown, Woods, Crable, Gutierrez (Henne's back-up before transferring), etc. etc.
Crable took a couple of years at Michigan to "get it", but came on like gangbusters his senior year (I think he was defensive captain). When he got to Michigan, he was something like 220 lbs. on a 6'5" or so frame. Really skinny for a football player. His legs remain thin, and he's much better going forward (rushing the passer) vs. going backwards (coverage), so I can see him evolving into the Rosevelt Colvin position over time, anticipating that he'll play special teams (where I bet he'll do well) and perform as a situational pass rusher, which the Pats will need with Colvin gone and Vrable getting older.