Shortcode is a killer feature!

People stay away from mailup because poor wordpress integration: i have to code for contact form 7 api integration because mailup plugin does not have shortcodes.
This is one of the reasons we push out clients to other services instead mailup.
Unfortunatelly some of them do use mailup and i have to look for hacks to make it work.
This tells me a lot about how serious mailup service is and how it cares about his users.