Submersible heaters?

I have two All Glass brand heaters. They are shatterproof and shut themselves off if the water level is too low, like during a water change. Plus they keep the water at a consistent temp. Definitely the best heater I've ever owned.
 
I've used Hagen Elites and Visi-Therm. I would have to say Visi-Therms are an excellent heater choice as they are very accurate and very forgiving...i.e not shutting them off when dropping water levels! :duh:
 
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