There is nothing wrong with being friends with benefits in my opinion, as long as both of you are sure that you actually want the same thing. If you know that you are not interested in this guy in any other way than as a friend, and if you're sure that he feels the same way, then you could just go for it, if it feels right. The tricky thing about being friends with benefits though, is that feelings might change when you start to get intimate together on a more regular basis. One of you might develop deeper romantic feeling for the other, and then you or this guy might end up getting hurt. So before agreeing upon anything, I think you should first be really sure about your own feelings, and then you should talk to him, just to make sure that both of you wants the same. There is always a risk that things might change, but if both of you are willing to take that risk it should be fine.