Love the Newsletter Integration (especially the SendFox one). However it's universal, because every single booker is going to be added to ONE list.
It would be more feasible to assign the booker to a specific newsletter list depending on the booking type.
This way I can build a funnel, e.g. someone is added to "5-min insights"-list if he books a usual 15-min call with me. Another one is added to "Workshop prep"-list if he books a paid workshop with me via TidyCal.