I have one of those. It takes a lot of work writing embedded C code to make it do what you want. In my case it was displaying a calendar and the moonphase. The default software is very bare bones. Battery life is 1.5 weeks for me when using ntp sync once a Day and a display update every minute without any further wireless communication.

I find the PineTime more attractive because it has an aditional heart rate sensor and a color display with similiar battery life.