I run a business centered around courses, and therefore needed a plugin to help me with attendees signing up for the available courses.
I quickly learned that this was one of the better plugins, and after having tried and tested a few others, I can safely say that this is the best one out there.
It does what I need it to, and the customizations are incredible. You can set this up exactly how you'd like and have it cater to your specific needs. Note, I opted straight for the "Hotel Edition" (despite being the most expensive), but I've not been let down and it's surely worth the money.
Frankly, the customer service alone is worth the price tag (these guys are amazing).