So I bought one of these on amazon, for one of my quarantine tanks. I gave the heater I had away with the 45 gallon tank to my friend.
I set the heater to 80. I was beginning a heat treatment so I was going to be bringing it up to 88 - wasn't really concerned if it was a bit warmer than 80. I came home to find the fish in the tank all dead. Seems they couldn't handle the 105 degree water very well. And the heater was still working!
That's why I love amazon - no hassle, easy returns. I actually requested an exchange. Since it's only for a quarantine tank and will be seeing limited use, I'm willing to take another chance....but there is no way I would trust running one on a show tank.