Beautiful fish dynomite... how long have you had it?
As for them not releasing toxins... well, that's just factually wrong. I'm not saying that they're a guaranteed tank apocalypse, but these fish will do what there physiology will do. A lot of factors come into play - tank filtration, size of the fish, individual fish biology, hardiness of tnak-mates, etc.
There are plenty of threads discussing how boxfish wiped out a tanks' inhabitants. On the other hand, I have a tetrasomus gibbosus in my 180, so it all depends on what kind of risk you're willing to accept
. I'm not saying don't buy boxfish, just be aware of the risk and the difficulty involved in keeping them healthy for the long term.
A previous poster claimed that any fish could be kept if the tank was properly set up. This may be true, but since we don't always know what a "proper tank set-up" is nor are we always able to provide such an aquarium in a home setting, I'd be a little more cautious in claiming that "any fish" is capable of being successfully kept in captivity.