What risks, Zoodiver?
I've kept O. Bimaculoides. I never had a problem keeping him, and he made a terrific pet. Very intelligent and very fun to watch. Like what has already been said many times, they need good water quality and a tight fitting lid. They are also terrific hunters, so a species tank is necessary. As long as you are careful with how you set up the tank and how you maintain it, you shouldn't have a problem. If you want more answers from experienced cephalopod keepers, check out tonmo.com.