My comments are limited to the Pro Stealth version. I had one explode after a week of use in the tank, with no water change involved. After checking around, there are several examples of Pros doing the same thing on the Net. The tank had no discus, but the explosion took out a dozen sterbais. I removed not only this heater, but all the others from my 40 breeders, and replaced them. This heater explodes into 3 pieces - not a malfunction, but a design flaw.
Since then, I've had 2 other aquarists locally report the same thing on our club website. I strongly suggest that you remove and replace these. It's a lot cheaper than replacing high quality fish.
Willie