Rated 4 out of 5 stars
Generally, the addon works as advertised, however, since some time Thunderbird asks me for passwords to Lightning calendars, which were also saved in Kwallet, previously. I'd like to help debugging/fixing this, but cannot contact the author:
The "Add-on home page" linked here on amo is a forum which does not exist anymore, the "Support site" exists but you cannot send a mail there because the google captcha doesn't load anymore.
@Guillermo Molina: please provide a working contact possibility.