I like it a lot. I've actually switched to FLAG for multi-chapter stories from ff.net. I like it a bit better than Fanfiction Downloader: the chapter headings and linked TOC are a little nicer. Also since the update, she's added little details like the original link to the story, and the date it was first posted and last updated.

The only downside to it for me is that I can't replace the title page with a picture of my own choosing in calibre. But that's a small price to pay for a nicely-formatted ebook.