I've never heard anything bad about the Hydor Theo. I had a Hydor Proquatics literally come apart in my hands once when I was turning the dial to change the temperature. I now use Visatherm Stealth. I also just bought a Rainbow Digital Temp Alert digital thermometer from Marine Depot that will sound an alarm if the temperature goes too high or too low. This evening, my Stealth heater died (it was at least a couple of years old) and the only reason I caught it before my tank got too cold was because I did a water change, so I noticed it.