The speed of my responses on emails (not waiting for replies).
Being able to customize each email address that is linked, which really helps me keep track who I am communicating with at any given time! If they have an API then it would be great if there were additional variables/options like how frequently do we send out this message? What's our goal here - what are some other ways i could use these features rather than just sending them straight away when someone signs up or subscribes etc.? It was very easy to set-up, but not as quick to implement once live compared to competitors similar services such as Hubspot & Marketo. Also having no ability to see where leads go after being sent through from us means tracking conversions isn't possible unless something else takes place before hand e g lead scoring / nurturing via nurture tools within the platform themselves.