For those that said he isn't great at either, the guy didn't give up a single pass over 20 yards all year, zero touchdowns given up last year. Two time all american. That is pretty elite from a CB.
The guy has a history of playing safety, both in college and high school, so its not that he is a complete novice at either position. He had excellent coaching from Phil Parker at Iowa. Just take a look at all the defensive backs currently in the pros from Iowa. Also, is an excellent returner.
My biggest worry would be his late season injury and even though most people recover these days, it may be a 2 year process before he is himself.