It has a nice, modern UI and is responsive/fast.
It was easy to set up a campaign and email to email adresses on a Google spreadsheet. When the emails were opened and the links in them clicked on, it showed this in my user dashboard almost real-time.
And it has a lot of integrations with email service providers but I only used Gmail and that worked fine.
Since more email marketing features are still to come, I'm happy I got the lifetime deal.