You're not thinking of diving at Lightning Rock off Porth Iago are you?
Those are probably some of the most, if not the most brutal currents you'll find on the whole of the Llyn - I think I remember hearing that Dario & Tecdave dived there once on the slack tide... might be wrong though - I foolishly took a kayak around there once... scary stuff..!
Not not there , haven't heard of that rock . Yeah places like that best dived in pairs at least if not a third ideally who will stay in the boat and pick you up if you end up getting pushed far away from tide, and be spot on with your slack timings.