The ability to monitor open rates etc is really great for us internally.
We are able use this data in our CRM tool so we can measure how well campaigns perform as part of their ROI metrics - I guess what would be best if they could integrate with 3rd party software such as Salesforce! If it's just internal monitoring then maybe no issues? They've worked very closely with us over several months now & have been fantastic at responding quickly when things go wrong (eg sending out an email which didn't include all contacts). Our main contact has moved jobs recently but he still helps support any queries.