Though the quality varies between themes, the add-on itself is superb. An absolute necessity if you like customizing your favorite websites.

Useful for custom dark mode in sites without it.

All of the functionality of Stylish without the shady data collection and selling.
It's also FLOSS which is a major plus.

It's OK.

seems to load styles slower on FF, like in Google Search, Chrome version does not have this issue.

Needs a "dark mode" (like on Windows)