I had a need for an exam component for two sites. I selected this one over some others. The documentation is pretty good and all emails were answered same or next day with very full answers. Granted, it's not the cheapest of components, but I've been using it for a few days now and it's been 100% stable. I was able to import a load of questions via CSV from a different system without issue, and am now in a position where I could get a new exam live literally within minutes.
Before I purchased I also noted that the change log had frequent updates, which shows that the component is under constant development, which is also very good.
I don't mind paying a premium price for a premium component, and this does exactly what it says on the tin.