They won't "accept ads" but they also won't pay for the extension, so I think in practice this is a good way to tell users "you're costing me money, go away."
I think this every time someone suggests an alternative to YouTube. Sorry but no one is making a video hosting service for users who both reject adverts and a premium subscription. And no content creator is going to work for free to post there.
You can downvote youtube videos without the extension, the extension just shows how many people downvoted a video since youtube took that visibility away a few years ago. It does help when there are shitty video recommendations and can ignore videos that have a bad ratio
The paid for feature seems to show the number of dislikes that have the extension installed, however what is shown is the estimated number of dislikes based on the actual number of likes youtube shows, so if the extension users have a like/dislike ratio of 50%, and there youtube shows 1000 likes, the extension estimates that there are also a 1000 users that disliked the video, even though there may only be 1 like and 1 dislike from the extension users, which would be very obvious that the estimate is very off.
IIRC, in the earliest days, the extension reported the dislike count that was still in the API but not surfaced in any clients. At some point after that, Google removed the count from the API entirely, requiring the current piecemeal approach.
I'm skeptical that it's of any use considering it's only going to be installed by people who specifically want to dislike. It seems more likely that the like/dislike ratio is going to be heavily skewed towards dislikes just by the stated purpose of the plugin and who it appeals to.
I don't think the extension is installed by people that wanna dislike, rather by people that wanna see the dislike count. I used to have it since it's very useful to see if something like a tutorial is a scam.
Also if I remember correctly, the extension was created before youtube completely removed the count, and it scraped the actual value from youtube to add it to the db while the count still was available
On the other hand, you also have to be a bit short sighted to be installed gargabage like "an extension so you can downvote" lol.