In reply to smbnji:
Sucking eggs I'm sure.
It depends where you sea cliff climb, 50m could quite conceivably be short. As I'm sure you understand that the height of the cliff is not necessarily the length of rope needed, especially if your anchors are fence posts/ quite far back etc.
Ab ropes all become hard to hank/ handle/ tie knots in with use, this is especially true if they get wet (and salty). Indeed I'd describe hanking an ab rope thats well used more as "folding". The thicker they are the worse this can be, and can at times create problems with descending too.
But if you're dangling about, a thicker rope gives you confidence. So too does a decent set up with rope protectors.
As for the differences between models, if you climb on granite, then luck (and skill in use) is probably as much a factor as model? someone with authority will no doubt be along for a comparison. Stick an ab down a popular descent on a bank holiday weekend and it'll get battered by every passing climber - prob being a little unfair to some climbers there - many do care about others kit. At least if the rope is long, then you can cut sections off - wear at the top and stuck in the sea bottoms... hopefully not the middle of course. If you climb a gentler rock, then longevity and model may correlate. I dont think I've ever had a rope that has "worn out" all over as an ab rope. They've always got too short or cut in half.