It’s not the guy in the trenchcoat next to you you need to worry about.
It’s the fact that some unknown entity owns/has set up the WiFi.
Anyone working with complex network setup and admin will tell you how much you can abuse owning the network a user is connected to.
The network guys at work never use public WiFi, not hotels or anything. Neither do I, even with my much more limited knowledge of network administration.
I mean a pianotuneR (as in a guy that tunes your piano) is pretty expensive.
These apps seem to be marketed as tools for professional piano tuners. And looking just at the screenshots it looks like it has a lot of tools and features outside of just showing the correct pitch.
If tuning pianos is your profession, paying 999$ once and writing it off as a business expense isn’t that far fetched.
(Better be a bloody useful tool though ;) )