I don't understand the second sentence... it's a lock-out tailcap, so twisting on/off should be possible.
As everything else by Surefire, it should be a mechanically sound design for 1 bar/10 m/30 ft of water, provided the O-rings are taken care off. It is not tested, though, so cannot be labeled with rating "water proof". Also, it cannot be tested by itself (d'oh, it's open on one end
), so only a complete flashlight using it could even be rated at all...