i have been using a cue with a uni-loc pin exclusively for three years, i play league once a week (twice last year) and practice once or twice a week for 3-4 hours a night, and i have NEVER had it come loose during play. i read somewhere that joint protectors are a MUST for uni-loc, so that stuck in my mind and the cue is never without them when it is apart.
i also agree with joey about the hit, my cue hits just fine. i would pay money to someone who can blindly tell me the difference between a uni-loc pin and insert, and any other steel and brass combo.