I have just released version 2.16.0 of the plugin. This fixes the problem reported by @Rid and adds what @ownedbycats wanted (which I don't remember seeing the first time, sorry).
The changes are:
- Fix: Fix removing the rating when rating is set.
- Change: Add option to not set font if already set on the device.
This should be announced by calibre in the next hour or so. If there are any problems, please report them here.