I didn't get that from this webpage. It seems like his extension just accepts all cookie requests and doesn't delete them.
“If you surf anonymously or if you delete cookies automatically every time you close the browser, websites will ask for that permission again and again, and it will soon become very irritating to click the same I agree buttons every day.”
The extension doesn't claim to delete cookies (and GP doesn't suggest that it does), but it's clearly targeted at people that are using technological means to deal with the problem rather than clicking "pretty please don't track me" and hoping for the best.
There's a big misunderstanding behind these "cookie" consent prompts. They are actually about overall data processing consent regardless of technical means - this includes cookies but also things like browser fingerprinting, IP addresses, etc which will persist despite clearing cookies.
Using an extension that automatically grants consent and merely deletes cookies every time would give you a false sense of security if the automatically granted consent allows them to use your browser's fingerprint or IP address to track you anyway.
Many websites and data processors violate this, but since that’s the case for those sites the only winning move is not to play.
> The information we collect includes unique identifiers, browser type and settings, device type and settings, operating system, mobile network information including carrier name and phone number, and application version number. We also collect information about the interaction of your apps, browsers, and devices with our services, including IP address, crash reports, system activity, and the date, time, and referrer URL of your request. ... We may also collect information about you from trusted partners, including marketing partners who provide us with information about potential customers of our business services, and security partners who provide us with information to protect against abuse. We also receive information from advertisers to provide advertising and research services on their behalf. We use various technologies to collect and store information, including cookies, pixel tags, local storage, such as browser web storage or application data caches, databases, and server logs. ... We use the information we collect to customize our services for you, including providing recommendations, personalized content, and customized search results
Given that I'm getting the cookies whether I want them or not, and deleting them whenever my browser closes, if this extension keeps the banners off my screen it's a huge net positive from my perspective.