The customer service that I have received from this product has been outstanding! There are many features to help with my daily work, but they also offer training so you can customize your setup without having to spend time figuring it out yourself or waiting long periods of time getting answers through e-mail support forums etc.
They do make sure their customers understand everything fully before going live as there really isn't much room for error in such important business functions as opt outs. It helps me get more done quickly each day by not worrying about missing any subscribers who want us to remove them from our lists.