MassFastmail

I moved from Gmail to Fastmail and the only thing I missed was gmass, the mass mailer. So eventually me and my colleague took the time to build it for Fastmail. It only has this one feature at the moment,but it's the most important one. Roadmap has Google Sheets integration, automatic followups, click tracking and more. While Superhuman and Hey are cool products, Fastmail has a proven track record and has a good price. How about bringing in the obvious features we expected to have in email clients a decade ago!

I'm a little confused. I want to be able to send personalised emails to a number of people, but I can't see if MassFastmail does this. I don't see the different between Mass Send and normal Send. What am I missing?