I primarily program Android phones, but instead of getting an Android watch I decided to get a PineTime in November. I've been happy with it. I primarily use

I primarily program Android phones, but instead of getting an Android watch I decided to get a PineTime in November. I've been happy with it. I primarily use it to calculate my BPM - while doing cardiovascular exercise, or resting, or whatever. I put GadgetBridge on my Android phone and hooked the watch into it and now get BPM charts of my workouts. I also connected it to my phone notifications so if I get a notification on my phone that I got a Signal message, the message appears on my watch. Cost $27 plus $12 shipping. I upgraded the firmware via Bluetooth - the newer firmware is said to do BPMs better (I checked before and after, and it does seem to). They sell a dev kit for the same price, although you don't need the dev kit to develop unless you're really getting into it. It's very developer friendly - you can write your own OS for it, or modify InfiniTime which is the OS it is shipped with. Source code is on Github. Have been happy with it so far.