The ability to easily add new fields, categories or products that are not yet available for our customers! Their support team has been very helpful with all of my questions as well (even when I'm just trying something out!).
They've helped us implement several different features from their platform into ours over time - everything works great together now!! We use it primarily because its easy enough for clients who don't know much about ecommerce sites but would like one themselves without having any technical knowledge at this point.