Eventually - and I mean the sort of eventually that's measured in seasons - one of these apps lets me register for a Rheem account (why they couldn't just give me a link to those webpages I could access in a browser, I do not know) and then crashes, but another one lets me get the water heater connected to the wifi (there's no ethernet hole on this 300kg tank of water plumbed and wired into the house, it uses wifi only like your phone or handheld game console) and holy shit it works
It actually works
About 50% of the time