If you're looking to keep a cat on the beach, then (much as I like them) I wouldn't recommend an Isotope. It is simply not made to take that level of battering and abuse. For example, the decks (and hatches) forward and aft of the crossbeams are not load-bearing. When someone stands on them (and if you store on the sand, somebody will), they will break.

Likewise, the Isotope was not designed for heavy chop. Its cantilevered bows give it lots of forward bouyancy. That greatly helps to avoid pitchpoling, but it also gives the boat a tendency to hobby-horse.

The Isotope does have several nice design features - an advantage of having been somewhat of a development class. Those include the flotation bags (even with both hulls full of water, she still floats), furling jib, righting bar, and the freedom to rig the controls however you like. I haven't seen any other cat with a "compression bar". It allows one to rig the jib lower (a more efficient sailplan) without having to put a lot of extra fiberglass in the bows. All-up, the Isotope weights about 280 pounds.

Best of luck with your choice,
Eric