From what I have seen, he definitely fits the early down thumper at ILB that is lacking on this team. Edds is more of that nickel/cover guy, Mitchell is the thumper ala what Tim Dobbins was supposed to bring to the defense. Essentially, Mitchell is replacing Tim Dobbins IMO.
I gotta believe either him or Spitler gets cut soon though . . . Miami isn't running with 10 LB's, and definitely not 5 ILB's, when in 2008 we ran with 3 (Crowder, Ayodele, Torbor) . . . actually 6 or 7 guys if you factor in that Trusnik can also play inside and Koa Misi has practiced there in the past as well.
Mitchell is also a very decent special teams player.