inkbird temperature controller and ehiem jager heaters are both reliable and a lot cheaper than the innovative marine, some of the saltwater stuff isnt too expensive and is the same for freshwater or salt. You probably have a couple heater lying around anyway so 2 heaters(any brand) and 1 inkbird is what i would use. Then when one heater eventually dies (sure you have been through your fair share) buy another eheim jager
I actually don’t have any extra heaters lying around. The Axolotls require really cold water compared to most freshwater and the Betta tank has a very small heater. Definitely down with cheaper as long as it’s just as reliable.