Still has a lot to prove on a passer. Scrambling QB's also tend to be injury prone at the next level. Just look at RG3 already in his rookie year. Plus Manziel is significantly smaller in size at about 6 foot even and 200 lbs soaking wet.
His arm strength leaves a lot to be desired, but I think he can improve that a little as he gets stronger. He does have pretty good accuracy at this point and has really progressed over the course of this year in that department.
It will be interesting to see how he plays next season if/when he loses his All-American O-Linemen and now that teams will be well aware of him.
*I'll add that he has massive hands and feet for someone his size. He wears a size 15 shoe and has roughly 10 inch hands. That's a big deal when it comes to QB's.
"The Dallas Cowboys have 2 types of plays in their playbook: Passing plays, and running plays." -John Madden