Rated 3 out of 5 stars

Though it is cited as "Works with Thunderbird 68.0 - *" its current version 3.0.3 does not work with 70.0b3 (64-bit), least on WIN10.

The extension's settings are not being stored.

This review is for a previous version of the add-on (3.0.3). 

You're right. This extension version is not supposed to work with beta versions after v68.
We are expecting more information from Thunderbird regarding the future of extensions in Thunderbird. There are many discussions on this topic between Thunderbird team and developers. We will probably need to move to a new standard (MailExtension), thus redeveloping all the extension.