I sorta agree with you, but in this case I ran that exact heater in two freshwater setups for nearly a year without any issue. I now have six of them in three saltwater tanks and gave a seventh one to a friend a few months ago. Several of mine have been running over a year without a glitch, which is BTW the recommended replacement interval on most heaters.Playing Russian roulette putting any kind of Amazon China product in your tank, I had a Amazon vivosun power head I used to mixed up new saltwater and didn’t realize the rotor started to rust until I lost all my acro colonies in my tank...lesson learned
In my educated electronics experienced opinion, anyone running a glass tube/nichrome wire element/bimetallic contact strip thermostat heater is the one standing on the edge of a cliff in a thunderstorm with a loaded revolver pointed at their temple. At least I'm hiding under a tree! You should warn them NOW!