Just got two Sonoff SNZB-02P and one SNZB-02 (ZigBee Temp and hygro sensors) and they are pretty good.

I left them overnight on a desk and the two SNZB-02P have converged to the same temp and hygro.

The SNZB-02 seems a bit less precise, humidity level is probably off by 5 to 10 points. And it is, overall, very basic.

The SNZB-02P is definitively an improved version and comes with a magnetic frame that can be glued or screwed in. Makes attaching and changing batteries very easy.