The thing is - if the Rams want to increase the chances of having a QB they can develop, they pretty much need to draft one in this spot. He won't start this season - and if Foles performs and they resign him may never start. But unless they try, if Foles doesn't star, or leaves as a free agent - they will be in serious trouble NEXT offseason. So I wouldn't mind them gambling here. Late in the third seems an appropriate spot..
Edit: That being said, I'm not sure Mannion is who I would have wanted. At least he's smart. Being football smart is crucial in a QB, after all.