Definitely pick him up as a handcuff to Turner for your own safety. Atlanta will get its RB points, regardless of who that RB actually is. Plus, groin injuries tend to linger, and as has been said, Turner has shown that he can miss multiple games due to injury.
Of the three backs, personally, I might drop Felix before Thomas...not because I think T. Jones is better, but because as things currently stand, his coach seems to like him a WHOLE lot more (Jones is actually playing and only has one RB to compete for carries with, as opposed to poor Felix who's stuck in some inexplicable/nonsensical timeshare).
It's really a coinflip, though, and long-term, Felix is probably your better option. KC simply has to let Charles be the premier back at some point. One would think, anyway...
(0.5 PPR, 12-team league)
QB: Vick, RG3
RB: McFadden, Matthews, K. Smith, R. Williams, M. Goodson
WR: Nicks, S. Smith, Britt, LaFell
TE: Hernandez, Pitta
DEF: Spot start (Cin in wk4)