Thank you! I am one of the founders, the accuracy will vary depending on how the person is wearing it, but regardless it will be well within clinically acceptable values for something like physiotherapy or rehab.

Yoganotch itself is new (2020) but we've been building these devices for a few years - have a number of peer reviewed papers published based on Notch (https://wearnotch.com/papers).

This looks like a very interesting solution! Is there a subscription fee for the YogaNotch app, as well, or is it just the one-time sensor purchase?

No, there is no subscription :)