In my opinion, when he's healthy, he is the most potent and dangerous weapon on the field. He can beat you in so many ways: As a running back, a receiver and even throwing the ball, he's got all the tools.
Yes, he has had some injury issues. But he would be the gutsiest player after Matt Stafford on the field.
For his career, he has averaged 4.6 yards per carry. He averages 53 catches a year. Also, he averages 91 yards per game.
A great compliment to Kevin Smith, he would be ideal to share the load between the two. Imagine him on 3rd down passing situations and heading out into the flat or on a swing pass and he'll get you the first down more often than not.
He's a clock killer and can strike from anywhere.
I believe he would be an excellent pickup in the free agent market.