Before I used it I would find myself checking FB sometimes throughout the day after posting something, because some part of me wanted to know how popular it was. The metric being front and center made part of my brain want to optimize for it. After installing the extension I couldn't really know how many people saw what I wrote except vaguely by looking at who commented or something. And as a result I found myself being less self conscious when I posted things - since there was no negative "not many likes" signal I found myself writing more what was actually on my mind. (Rather than what I thought my friends wanted to read).
I hear what you're saying about being at an information disadvantage - but that only matters if "number of likes" is something you're trying to optimize for. I think thats a pretty shallow way to live your life. There's lots of other reasons to speak and listen than how "liked" those words are in the moment. If we rated food the same way we'd only eat junk food. If we raised children optimizing for likes they'd grow up stunted. If we rated academic papers that way we wouldn't even know about the replication crisis.
Ironically when I couldn't see the number of likes on FB, I think what I posted was more interesting as a result anyway. It was certainly more authentic, since while authoring I spent more brain cells thinking about what I wanted to say rather than obsessing about social perception. Every person who's opinion you're worried about when you write makes your writing about 1% worse - which isn't much, but it adds up.
The only real downside was that the extension didn't work on my phone, so I'd end up seeing the numbers of FB likes there anyway. I ended up deleting FB year or two later because it was still too addictive, but I think this extension is a great idea.
It doesn't cost anything to try it out. If you're not sure, run the experiment and see if you have the same experience I did.
If likes, followers, etc. were private (that is, you could see who liked your post but no one else could), you wouldn't worry about what others would think of you based on those numbers. But since they're public and prominently displayed, we equate those numbers to our social value and end up with undesirable effects like comparing ourselves to others and focusing on what would get approval rather than what's authentic.
It would probably be simpler to just release an adblock filter instead of having another redudant addon, but I'm okay with its purpose.
With that said, I believe it can function similar to all those no-procrastination tools; allowing those that want to stop the feedback loop of likes to ween themselves off of it. More of a personal growth tool than a societal solution.