I like that it allows me to send out mass emails with very little effort at all! The customer service has been great for us so far, but they could definitely improve their website in order to make things easier (and more user-friendly).
We have used this product primarily because we needed something fast/easy to use without having to spend hours creating an entire database ourselves from scratch - which would cost thousands or even tens of thousand dollars depending upon what you want your list to look like.