They don't need another RB. They are 3 deep now with RBs who all have complementary skills. Akers on early downs with Evans in rotation and Williams on 3rd downs. Evans is a grinder type RB very much like Michel, but Evans is a bit faster, more elusive, and a better receiver. IMO Evan's forte will be running between the tackles and with Avila and Shelton they have the C and RG to run behind. Akers can run inside and outside and is running as good or better than before his injury.
No they don't need a RB. People are dismissing Evans because of his draft position. But most boards had him as a 3rd or 4th round pick, so IMO the Rams got a steal. Had Evans been taken in the 3rd or 4th round the media and fans wouldn't be talking signing a vet. Evans gives them that tough inside runner much like they had with Michel. The only thing Michel does better than Evans is pass block. But Evans is a better receiver and faster and more agile than Sony. Michel was a big part of their Super Bowl run, and IMO it's why the Rams traded up to get him. Evans gives the Rams the complementary RB they had with Michel to pair with Akers. If they can't resign Akers next year then Evans gives them a legit #1RB.