For anyone interested in modding the F-91W there's also The Ollee Watch, a replacement PCB which adds even more "smart" features.
It has ... uuuuuh ... blackjack?
Is it did that get implemented solely so someone could say "I'll make my own watch, with blackjack and hookers"?
The developer also recently posted on Reddit that he’ll soon be adding third party app support
Sensor Watch is the non-phone-connected OG:
https://www.sensorwatch.net