Man, sorry to hear that, hopefully your tank will recovery soon and get some of those corals back.
Most of the heaters I’ve used are Eheim/Jager, and Titanium ones with controllers and actually gave a try to a Cobalt Neotherm in the Nuvo 20, while it’s been strong for a season and a half I’m not sure what will be next (knock on wood) and actually I don’t have a monitor in there, I might going to order one. Being said that seems like in this industry nothing is 100% fail safe, had pumps fail on me, chiller fail on me, a Ranco Controller, gaskets, and luckily (knock on wood again lol) never had an ATO fail on me, but have heard horror histories of anything already.
I’ve learned that in order to succeed we should always try to have backups, pumps, heaters, powerheads, plumbing supplies, battery powered pumps, battery backups, ATO’s, even lights, smaller tanks (ha! Is the reason some of us have a hardware store in our basement or garage
just for the hobby) and more important, and I’ve learned this from Adam, be redundant on monitors, sensors, float valves, mechanical or electrical, this help us relieve or try to mitigate some of the issues it could arise.