> I'd think combining 1 and 6 (O₂ monitoring and waterproofing) would be difficult.

By O2 monitoring, they mean "blood oxygen through skin via LEDs" - there's no impact on waterproofing from that (as the Apple Watch demonstrates.)

The Pro version has a better screen (still segmented but more), RGB LEDs and an infrared sensor.

my experience with a sensor watch has been terrible.

imagine breaking a $3 watch that is not quite as indestructible as people think it is, but it is nonetheless pretty robust, and then trying to shove something 100x glitchier and 5x as expensive into its case...