I had one for about a month. It was a great fish with lots of personality. The cowfish would eat anything, but was a weak swimmer, so feed time was high maintenance as I fed all of the fish at one end of the tank, and while they were distracted, I target fed the cowfish at the other end. It was also interesting to watch it eat worms out of the sandbed. Cowfish blow a jet of water from their mouths to clear the sand and expose worms to eat.
Unfortunately, my cowfish would constantly get stuck to the intake of my powerheads, even with guards and prefilters attached. I was constantly turning the powerheads off to release the cowfish, but it got stuck one too many times, and swam awkwardly after the last time. I moved it into a hospital tank where it lived for a few days and then died.
Just give your cowfish a little extra TLC, and enjoy its personality.