I have been using a Cubot Mini (4") for sometime now (1+ year), and am pretty happy with the experience overall. Feels so good to have a phone that fits in any pocket.
Is it possible to screw a belt clip there? And I don't mean in a case, but physically attached to the back of the phone with screws?
Some Chinese work phones have that feature, and it's stupidly addictive to be able to clip your phone anywhere!
Battery life is pretty good; I charge it at night, and usually is half-battery. My usage is pretty decent, but mostly on wifi.