I have read that aquarium heaters are essentially 100% efficient. If so, watts are watts, and it shouldn’t matter how you get there. I toyed with doing a loop off my water heater, but since it’s an electric unit, I figured there’d be no savings. I don’t frankly worry about physical breakage - had plenty of heaters stop working, but none actually break. If I was dealing with truly huge water volumes, I’d probably add a zone to my house heating (oil fired boiler). There have been occasional threads on how to do this.
The other thing I have noticed is that 1” acrylic on the current 450 is a far better insulator than 1/2” glass on the prior 265, and both require about the same total wattage. Plus bigger tanks have a lower surface to volume ratio which also helps.