I don't use yocto or buildroot, so I can't really comment on either. I also put together my own updating mechanism which uses A/B booting (so it boots from part

I don't use yocto or buildroot, so I can't really comment on either. I also put together my own updating mechanism which uses A/B booting (so it boots from partition A, updates into B, makes that active and then tries to boot into B. Once successful, it switch A and B and the cycle starts again). It's deeply integrated into the rest of the system (like the success condition of updates and timeouts waiting for that condition). The fear of accidentally bricking all live devices motivated me to build something I truly understand and is minimal (it's core is at most 200 lines of python). Ultibo seems pretty nice, although I only read a bit out it and didn't play around with it. I'm a big fan of small systems and fondly remember writing Pascal back in the Borland Pascal days.