We have a cowfish and he is more entertaining than I ever thought a fish could be. He bobs up and down, spits water at us (not a problem - we have a canopy), follows us around, will eat out of our hands, etc. He came with the tank we bought so that's how we ended up with him.
With regard to the issue of being delicate, getting sick, nuking the tank, etc. maybe our fish is exceptional but we don't find any of those things to be true, and believe me, if a cowfish were going to die, or nuke a tank, it would have been this one over the last 2 weeks.
2 weeks ago, our 240 gallon tank cracked along the front from corner to corner and all the water came out. The cowfish was laying on the floor along with some other fish. We scooped them all up and got them in our 20 gallon QT - roughly 30 different organisms between fish, crabs, anemones, etc. Way too much for such a little space. they were all in there for about 4 1/2 hours until we could get most of them moved to our LFS until we could figure something out. He was fine.
We kept the cowfish and a few other fish at home in the 20 gallon. Still way too many fish. So, went and picked up a 39 gallon to have as a backup and got it set up. While we were doing that, we wanted to use as much of the existing tank water as possible - as we were siphoning it out, he first got stuck on the siphon and then panicked when the water got too shallow. I'm talking full-on panic. I scooped him out in a pitcher I had handy, hoping he wouldn't kill all the fish and himself. Put him in a larger bowl until we could get the water all moved into the new tank. Still total panic until we got him in the tank.
Since then, he has been subject to every rookie mistake we could have possibly made. Every water quality issue you can imagine. Still going strong.
Then the tang that was with him got Ich, and so did he and 2 other fish. Wanted to get them into QT tank with no sand, etc. so we did that, in a 10 gallon tank this time (the 20 gallon got dropped and broken in cleaning). We did everything wrong that you could do to eliminate Ich and whatever the black spots were on a different fish. Hypo, prazipro, Ich treatment., all kinds of things we probably shouldn't have done. Of course, no biological filter so we're doing water changes every day to keep the ammonia down, etc... 2 of the other fish in the tank died, which honestly is not a surprise considering how crazy it has been.
He is currently bobbing up and down happily spitting water, tail all fanned out as I write this. So, I'm going to respectfully suggest that the risk of a cowfish nuking a tank probably exists, but I would call it possible, not probable.
So, if you want a super entertaining fish with a great personality, this one should definitely be considered!
