I saw one in an LFS
about 2 years ago--a real mimic octo. It was probably one of the most amazing animals I have ever seen. Reminded me of a lion fish. I tried an octopus once. I did not have a lot of experience in the hobby. The local LFS
ordered it for me. I had high expectations and when I saw it, I was a little dumb founded. It was really small and hiding. The owner of the shop packed it up for me in a bag with very little water. It looked like a spider and I think it was very young. I got it home after a 20 minute trip. I kept it in the paper bag so as not shock it, but when I took it out to float it in the tank water, the water was cloudy and dark--it inked. I didn't realize that the ink could be fatal to the octopus in a small body of water. It was stiff, but I tried to acclimate. When I released it into the tank it sunk to the bottom like a stiff tree branch and was dead as a door nail. Really disappointing--I was young, maybe 12.
I did some more research and knew I wasn't prepared for an octo. They don't live long and hide quite a bit. They need a dedicated tank as you know, and I would consider them difficult to maintain if they don't end up crawling out of the tank through the smallest of openings.
Give it shot, or if you want something more active try a cuddle fish: amazing creatures as well.