There are a lot of fakes out there, so beware of "good" deals.
They wear out pretty quickly, especially between the toes, and more so if you don't care for your nails. I find they do fill with sand when standing in the surf. But overall I do like them. I have always had the middle range ones with the luggy sole, but mesh uppers. I think those were normally called the KSO, but maybe KSO sport?
They are very different to wear though, so if you rely on your shoes for any support at all, they will hurt you pretty quick. I've got it on good advice that they are a great method for celibacy, Most of the women I know can't stand the sight of them, so that may or may not be a factor for you, my wife detests them.
To be honest, I don't really know if they are worth it, I like them, but not for any rational reason. For almost any purpose there is a better shoe. My main use is if I'm rock fishing, but there plenty of good rock shoes that are easier to wear and cheaper.
I got my first pair at least 8 years ago. I'm on pair three, and they have been repaired once so far, glued part of the sole back on. I find very few shoes will survive long duration submersion though, either that or there is something in the water here.