Other than CMD, I doubt many (if any) of you have really seen him play. I admit I probably haven't seen more than a few mins of him over a couple of games.
I watched this clip (and a few others) though and can see why teams would be interested. He good size and a nice arm, can throw with touch and seems to throw downfield pretty well. His footwork in his drop backs is good. He shows good hand fakes on PA passes. The write ups on him are not bad at all and it seems the consensus is he is a middle round pick. While Dooms (the great scout that he is) points out 54 picks, he doesn't point out that he had only 23 his final two yrs (23 might seem like a lot, but that's on nearly 700 attempts),...he threw 52 tds the past two seasons... or that for his career he completed almost 65% of his throws
He needs more coaching and experience. It also wouldn't hurt to play with a better supporting cast, the teams he has been on have been pretty mediocre at best.
Sean Mannion 2013 highlights - YouTube