In the daily FBG email, they commented on Johnson signing his rookie deal and added their take in the quote below.
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Johnson is a big back who can grind down opponents as the game goes on. He's a determined runner with an efficient style. Johnson's not going to break any ankles in the open field, but he can run through arm tackles consistently. He'll make for a power change-of-pace back behind Andre Ellington this year.
I found the FBG take to be interesting. I have read a lot on Johnson and most sources view him as something other than a power runner, despite having ideal size for such... Most see him as more of a RB that is solid/good at many facets (speed, receiving, blocking, etc.). The little I watched of him (disclaimer: I am no film expert), I came away impressed with his feet for his size and his jump cut.
Also, the video posted earlier in this thread of Arians and the ARI GM talking about Johnson was interesting, and indicated that this duo views Johnson as more than change-of-pace back, and instead something possibly similar to Forte (though probably wishful thinking and coach speak, yet there are size and skill set similarities, imo). They see him as a guy that they can bring into the game without changing up the offensive approach.
It will be interesting to see how the ARI RB situation plays out and how Johnson's skill set transfers to the NFL (coming from Northern Iowa).