Also, one last tidbit: I know the idea was to stay away from the more expensive devices, but many Apple and Android watches have built-in BLE central capability so they can scan and connect to peripherals without having to go through the phone. In later models, they can even scan in the background and update complications.
Again, not remotely as cool as building one's own device!
The DevKit is mainly there to allow easy access the SWD pins. It can be flashed via a Pi: https://wiki.pine64.org/wiki/PineTime_Devkit_Wiring
Aaron Christophel (go-to guy for hacking wearables) has a video on flashing them via an ESP32: https://www.youtube.com/watch?v=Iu6RoXRZxOk
For OTA flash, some folks have had good luck with https://gadgetbridge.org
For those interested in going the cheap-o activity tracker route, here's another old thread on Hackaday, featuring Aaron. More good info in the comments: https://hackaday.com/2019/02/20/custom-firmware-for-cheap-fi...
Also, one last tidbit: I know the idea was to stay away from the more expensive devices, but many Apple and Android watches have built-in BLE central capability so they can scan and connect to peripherals without having to go through the phone. In later models, they can even scan in the background and update complications.
Again, not remotely as cool as building one's own device!