Sorry for the length it took me to respond.
Anyway, I was just doing some quick research on the subject of these cuttlefish. I converted their common maximum length (8cm) into inches (3 inches), with this knowledge I realize that a Flamboyant Cuttlefish would very easily be able to be housed in a small aquarium, generally comparing them to more commonly available species of cuttlefish (Sepia officinalis), my reference which is Liveaquaria.net; I knoiw this is not the most refuttable information available, but I trust them. Regardless, the information provided says that their cuttlefish should be kept in a 70 gallon aquarium or larger, and can grow to a maximum size of 1'4", so generally comapring I would figure that a Flamboyant cuttlefish would be able to be kept in a minumum tank of 20 gallons.
Now the point of their flesh being too toxic for a reef tank, due to the fact of expiration. As far as I'm aware the poisons do not diffuse into the surrounding water at the moment of death or afterwards, albeit, after I finish this post, I will be looking to emailing a marine biologist knowledgable with cuttlefish.
Joel.