Another niche: swimming pool owners. Although it’s only worth it if I can link it to an action eg add acid but that feels a bit dangerous for diy project! Maybe a sms to add he acid and how much is good enough
I don't need perfect accuracy, and checking it manually isn't overly time-consuming. It IS tedious enough that I only check it about once a week though, and I'd prefer to be checking it more often. And bonus points for being able to automatically track it & easily graph it, too!