This looks really good! I'm a Meeter user so it's a real use case I have already spent time looking for solutions to.
I agree with other commenters though - I'd pay a one-time $10, but $10 per month seems unreasonably high. For perspective Meeter is free, and Spotify is $4 for a family of 4 (in my country).
Maybe it could be part of the bundle at https://setapp.com/ or similar? Or you could have a set-your-own-price monthly sub?