I personally like the ease of setting up events and registration pages, clean data capturing in reporting, and the ability to push those reports to a shared company-wide portal.
You can make your registration event pages quite robust with information- that is probably the best PRO of the software. It is also great that it is Cloud-based like all software should be these days.
Flex is a great addition to the product - super easy to use and aesthetically pleasing.
If you use the legacy system, not only are you wasting your time learning a system that will be eliminated, but your events will disappear after the change as they can't be transferred.
Poor communications with management, no intentions to resolve customer concerns or address complaints.
Limited capabilities in e-marketing (no A/B testing, no series/time-based emails, no way for subscribers to change frequency of emails - you're either subscribed or opted out).