This addon modifies a lot of things on Youtube's pages, but I only consider one of those changes a good thing. The others are odd, or even bad.

First the positive one: it allows you to view more thumbnails on the mainpage. That's great!

However, along with that singular positive thing, comes a lot of questionable ones. For example, the default settings make everything about the page layouts look older, less modern, even ugly. Why is that? And even though you can disable some of these changes, there are things that it messes up permanently. Like the latest Youtube posts. They get truncated to just a few words each, and there is no option to change that behaviour. Also, playlist thumbnails are unaffected (= remain huge) despite everything else shrinking. The layouts just become erratic and mismatched.

I would not recommend this addon. If you just want to see more video thumbnails on Youtube's main page, there are better ways to achieve that.