I've been using Dunlop straplocks for 10 years and not once have they ever failed me! One of my favourite things of it is that the actual part that drills into the body is just like a normal strap holder and would accommodate another strap (if you were silly enough to forget the strap you have with the straplocks on it, as I do every now and then! :P )
The screws it comes with has been significantly bigger (and sometimes a lot longer longer) than the original screws on all of my guitars. Some of my guitars required a little bit of drilling as the original screw holes were way too short for these new ones.
The only problem I can see anyone having is trying to put the straplock part onto the strap, which was a bit difficult on my first go. To do it, I now use a screwdriver (or a spoon!) to help push one of the metal parts into place to hold the strap. Once that done you're ready to go!
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