I flashed the firmware posted by Rick (from Banggood, V1.0.1_V5, 28 Aug 2017).
The problem with Google Play Services is resolved (automatically updated).
The rom is not rooted but, with a procedure a bit complicated, I managed to root the system.
The only two problems I have encountered are:
1) the time zone in system settings does not change: at every boot the system automatically sets Shanghai GMT + 08:00; thanks to root, I have deleted this incorrect setting in the build.prop file.
2) portrait default orientation is reversed (home physical key is up). I do not know how to fix it.
For the rest, the tablet works perfectly.