The data is accurate (as far as I can tell), timely, easy to use & customize reports/reports are good! Nothing so much at this point but they could be more user friendly in terms of layout or ease of navigation through their website - which seems like it would help with customer service too because you'd have an easier time figuring out what's going wrong when customers complain about not receiving emails that they should've received etc.
Great product overall though if your looking into having someone handle all aspects of email sending then definitely consider them. They're great people who care very deeply about getting our messages sent correctly every single time we send one. We never had any issues using their system until recently where some accounts were being set up incorrectly resulting in us losing revenue over $3000 per week due to missing opportunities from these errors!