[noirscape]

Keep in mind that the type of people who are going to use this extension will also likely only view a specific domain of video content. While yes, it'll be a very small sample size on the whole, those users will still be representative of the broad strokes for that kind of content.

Like, let's say that the audience is specifically going to be interested in tech content (not too big of a stretch). With tech content, there's a couple of standout creators that are... at least somewhat universally interesting/viewed (ie. Tom Scott). As a result, you can fairly reliably conclude that any dislike count on those creators will be at least percentage-wise accurate enough. OTOH, let's say that this audience is not interested at all in "prank videos". (This is a personal bias - this is something I cannot stand myself.) As a result, those videos will have less registered data on the backend, and as a result the dislike counter for those extensions will be less accurate as a result, but for the audience that has this extension installed it won't matter.

Others have already pointed out that the extension has about half a million users already, but even if it was as low as you are suggesting, it can still be very useful in that specific criteria.

I don't think anyone is doing serious usage analysis on dislike/like counts with the data from this extension, people just like having a general idea on what the ratio is.