What do you like best?
Works well with large amounts of email going through, using external relays. Really powerful system, with a tonne of API calls and automation hooks.
What do you dislike?
It's only my personal opinion but we had a basic system beforehand and needed more help than we got. You don't get much support when dealing with issues like slow speed sending, software crashes, etc. They shift blame on MTAs now and again... I wouldn't recommend it to anyone who isn't 100% sure they need it.
It's also real expensive. For a standalone system that you can install on your own server, your company will have to have deep pockets.
Recommendations to others considering the product
Make sure you really need the extent of what they offer as we found it a bit much.
What business problems are you solving with the product? What benefits have you realized?
Needing to target, segment and measure how our campaigns do.