Well, nrf51 was good choice few years ago, but for that price, and if you get it fast (says ships from UK) and you really get what is described (you often get other random chips inside) then it make some sense and you can learn a lot with that ;-) H band app means it can be nrf51 with 32KB indeed, there are lot of firmware files for that app for nrf51/32KB. I wouldn't bother with nrf51 today but I guess it can be done with lot of pain. Try to figure out firmware version or hw model number, if you can get firmware update you'll know what SDK/Softdevice it is so you can better build DFU package for that. It will be something old so you can't build Espruino for that without doing some changes and backporting (or getting old 1.x espruino version from git) or updating softdevice and bootloader to something recent (which is tricky to do without taking apart). With DS-D6 I started with espruino 1.87 which was still using SDK11 but maybe you need something even older. Or if it can be opened easily without damage, using SWD to reflash it saves a lot of effort. Anyway, I guess "Official Espruino Boards / Bangle.js" is not best topic for discussing all that.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Well, nrf51 was good choice few years ago, but for that price, and if you get it fast (says ships from UK) and you really get what is described (you often get other random chips inside) then it make some sense and you can learn a lot with that ;-) H band app means it can be nrf51 with 32KB indeed, there are lot of firmware files for that app for nrf51/32KB. I wouldn't bother with nrf51 today but I guess it can be done with lot of pain. Try to figure out firmware version or hw model number, if you can get firmware update you'll know what SDK/Softdevice it is so you can better build DFU package for that. It will be something old so you can't build Espruino for that without doing some changes and backporting (or getting old 1.x espruino version from git) or updating softdevice and bootloader to something recent (which is tricky to do without taking apart). With DS-D6 I started with espruino 1.87 which was still using SDK11 but maybe you need something even older. Or if it can be opened easily without damage, using SWD to reflash it saves a lot of effort. Anyway, I guess "Official Espruino Boards / Bangle.js" is not best topic for discussing all that.