I like how easy it is to use, and how customizable it is. It's not as intuitive as some other programs, but I think that's because of my lack of experience with this type of program. You can set bandwidth limits for specific IP addresses or ranges, as well as per user. This makes it very useful for organizations who want to limit certain types of traffic.
I don't like that you have to pay extra for additional users. If you're looking for something simple and cheap, this might be what you need…