Too bad they don't stay cute and small for long. They get very large and will eat a variety of things, including (according to Fishbase) fish (as well as a variety of inverts). They fall into the "panther grouper" class of fish- cute and cuddly, but become huge and not as cute.
My LFS also will not stock them, after the having the same experience moorishIdol described happen at his LFS. I also had a customer have a kill off in his tank (he bought one at another LFS), and came to
us for answers on what to do.
They won't all die (or live) and poison a tank, but it is a possibility and a reality. Hopefully we don't ever see a post from anyone on this.
I remember a post from a guy who was sure he could learn a bunch by keeping a sea apple in his tank. Wrote a long post on how they are SO misunderstood and beautiful. The thing spawned (though he didn't know it at the time) the next day (if that) and freaked him out. Went back to the LFS ASAP. Nothing died, but he realized how easily he could have lost all his fish by playing with fire.
Keeping in mind that many people avoid them, and many people who buy them don't visit boards (or know what happened if their tank died anyway considering LFS don't usually tell them things are poisonous), it might be a rather limited dataset to have confidence in or draw many conclusions from.
I have come to adopt this philosophy for the hobby: your experience has very little impact on my success. Even if no one in this thread has had a poisoning event, it does not mean that you won't, it is a scientific fact that it can happen...and as soon as you have the greatest fish in the world, it probably will. Murphy's law. But you are more than welcome to take that risk.
But I would be wary of being too confident. Dolphins are really cute too, with those smiles and happy go lucky attitude. But scientists are learning that they are rather mean critters in their own right. There is something to learn from that. It is risky to be too anthropomorphic.
Best of luck.