I put some of those frost free outside faucets on my place. The faucets also included some sort of check valve. The next spring the check valves were junk and made a considerable obstruction to the flow of water. I dismantled both valves and removed the damaged parts. Later I determined that both valves still obstructed the flow of water and removed them, replacing them with ball valves and reverting to an inside drain.
YMMV