Edit: actually I guess that is not the PineTime in the photo, knob is on the right side.
Typically they are about as flexible as calculators, but this CPU has been shown to run Doom, so it's a general-purpose computer too :)
I don't know if this is something I'd want to build, but I spent 5 years at an outfit that designed/built a variety of fitness devices like this, including some of the consoles on gym equipment you may have used.
You mentioned 'figuring out Bluetooth (BLE, please)" in another post. What are you having trouble with? The sample code in the Nordic SDK is pretty good in most cases.
I will have to port the NimBLE stack to Tock OS, and that's guaranteed going to be complicated, so someone who knows at least how Bluetooth works in general would be invaluable.
I will sell them together with a Bluetooth wheel/cadence sensor once I figure out Bluetooth.
I'd be curious on design choices like waterproofing, battery life, things like that. Also I think you mentioned your site is getting worked on but pictures to clarify what it is about would help sell it.
The web site was put up before I started the firmware work, so obviously no pictures :) They will come once the project becomes more useful.