This is very easily one of the best add-ons for XF.
If you're nostalgic for the days of Myspace and early Youtube which allowed users to personalize their pages with custom CSS, backgrounds, and colors, this add-on is for you.
I've seen this add-on in action on other sites that aren't my own, and on every site, the users love it.
The developer is friendly and inhumanly fast at responding to bug reports and other inquiries. You should give them your money, because developers like this make the Internet a fun place to spend time on again.