The only grievance I've had is that it has reverted back to free edition (once), but that was due to a bug in their new upgrade system, which was resolved within a day (got updates via email about the progress). It is definitely a must have for me and my site, even the J! default compatibility is so good that it works brilliantly with JFusion (even though JoomSEF is not officially supported by JFusion).
It is a bit annoying that there are many paid plugins, but the support I have gotten from the ones I have purchased made it worth the few bucks I had to cough up.
But installing it should not be done lightly. Be prepared to read through the instructions, check out the FAQ etc, as it is very easy to take a wrong turn, and end up with tons of 404 pages. In most cases, these are easily solved, and the most common ones are covered in the FAQ. It should not be taken lightly, it is easy to mess up!
The component it self does just what it is supposed to do: Create a community for your website, let your users interact and connect with each other.
Their support forum is very efficient. My first support request was answered within 24 hrs and one of their support staff was on my site to explore the error within the same time. Second request was solved within the same time limit and my 3rd request was also solved within 24 hrs within posting the issue.
And even after all my whining posts on the forums the support staff still remained polite and helpful. This component is highly recommended from me and my users!