On another forum, the Dunlop/Schaller debate has been waged quite a bit. There seems to be pros and cons to each, with loyalty to either spread pretty much equally.
The Dunlops lock like a socket attaches to a ratchet wrench, you know, with that little spring loaded ball. Consensus says that this mechanism needs to be periodically lubed to keep working. No biggie. The locking piece attaches to the strap with a "C" clip so it'll never loosen or come off. I have Dunlops on my Les Pa....oops, ..uh, non-EBMM guitar. I couldn't use the stock screw on one of the strap pegs because the head was too large to fit through the new Dunlop peg. I had to use the screw that came with the Dunlop, but the threads were too small for the hole in the guitar, so I used the old hole-remover trick (toothpicks and glue). Now it's stronger than before, even with the smaller screw. It's true though that if the little spring loaded ball mechanism fails, or the release button is pressed inadvertently, the guitar will fall, just like pressing that button on the back of your ratchet wrench, the socket falls off.
The Schallers (I've heard) have a U shaped "cradle" that allows the guitar to still be held up if the locking mechanism fails. This means that, if that U piece is oriented upwards, you'll have a backup system to save the guitar from falling. The cons of the Schallers appear to be that the piece attaches to the strap with a nut that has a tendency to work loose. Tightening it well with some Loctite will most likely help. The button also has a tendency to scrape and wear the U shaped piece, which may also lead to failure if not lubed.
On guitars with one-piece angled headstocks, strap locks are a MUST. You drop a Fender or EBMM, you get a chip or a ding...you drop a Les Paul, you get a broken headstock.
Alot of people swear by the little rubber washer from a Grolsch beer bottle. Slip it over the button after the strap. Someone also uses the little plastic thing that keeps your loaf of bread closed.
Adam