It's free, and the project is active and well-maintained, which means lots of updates are made to the software almost every week. Some of the features are basic (like only showing a list of functions), but other features are quite advanced (such as having an auto-generating class diagram). I don't like how sometimes the website loads really slow, especially when there are lots of comments/reviews in between.
It would be nice if the comment box could be moved outside of the page on mobile…