Just curious. This my first iphone that I only bought a bumper for, as the back shell seems pretty sturdy! The bumper would be to protect the screen from drops or scratching if put on a table or something. Is your 5C currently in a case?
I bought a case for my 5c before receiving the phone itself. After getting the phone however, I don't really find a need for it. The phone is incredibly sturdy, it just doesn't feel needed. Perhaps if you want to keep the plastic housing from getting scratched you could use one, but the phone is by no means delicate.
My wife doesn't rock a case on hers. I had one before switching to the 5S and didn't really see a need to put a case on it. Now I feel the same way about my 5S.