As of November of 2021, I ("technical data-security" person in public sector) see the legal situation for this addon as follows:

Lets start with a big con about entering legal contracts by surfing in the world wide web:

- Absolutely violates the " informed consent" required by GDPR by sometimes giving consent but hiding what I actually agreed to. Legally, neither the user nor the website now know if anyone is at fault for aggregating and using personal data. I can neither exercise my rights to be informed or correct data that was collected, nor can the website owner use or sell my data in good conscience.

- The developers website acknowledges this schism: "Please educate yourself about cookie related privacy issues and ways to protect yourself and your data. For example, you can block 3rd party cookies, install ad blocking extensions and then block tracking tools, delete browsing data regularly, enable Tracking Protection in your browser etc."
Which is the right way to handle cookie banners. This is the worst way for all parties involved. To reiterate: even the website owners get a poisoned gift by receiving non-legally-valid consent, and the user waives all control over their personal rights without even knowing, how that might hurt him or her whenever this add-on allows some tracking cookies to be stored.

Pros:

+ Visually, seems to work. (Legally, see above. Browser Cookies are not about cookies or computer science, but the actual subject matter is keeping others from knowing what kind of stigmatised interests or ridiculed condition you keep to yourself or a very limited audience. By not caring, you shoot yourself in the foot.)
+ The developer actually reads this and reacts to it.

UPDATE:

Starting in December, this Addon will probably need to register as a "Personal Information Management Systems" (PIMS) in germany, to finally become legal. Let's hope that it won't be an extensive and thereby expensive certification. If @Kiko fails to do that, this app will still work ins legally gray area are finally become illegal in germany and should regionally be blocked to avoid anyone sueing Kiko or the end-users.

The EUs info on that:
https://edps.europa.eu/data-protection/our-work/publications/techdispatch/techdispatch-32020-personal-information_en
This might even of interest for power users or people who actually read EULAs.