I like how our agency has a helpful team to assist in billing, integration, setup, and other technical information we would need. We have a Slack channel our agency shares with Opensend, so getting support is quick and easy. We also have dedicated reps for each of our Opensend clients. The initial setup was very easy, as we had an Opensend rep walk us through the process.
I like that Opensend provides a service I didn't know existed, which is really helpful for lead generation. The daily email delivery works well, and I value the ability to suppress known contacts. It was also very easy to set up.