They look alien! Mine spend most of the day in and out of the rocks and only really venture out at night. They're like turbo snails on steroids (they can cover a lot of ground and obstacles present no challenge whatsoever). They abhor high nitrate levels, but other than that they're fairly easy to care for. As long as your tank is established and there's plenty of algae (etc.) no nibble on - they'll be content.
Here's "Oscar" with 4 Halloween hermit pals joining "Homer" (the other abalone) in my tank. I highly recommend drip acclimating your abalone for 35-45 minutes prior to introduction. And you'll note Oscar is in a strainer: when these guys decide to stick to something, they're not coming off for hours. So I can just slip the strainer in the tank and wait for him to crawl out if need be.