Better user experience than some big names
Inbox was one of my early investments when I joined Appsumo a few years ago. However, I did not get to use it until yesterday because I needed to launch a newsletter campaign.
I left it on the "shelf" partly because of some of the reviews I had read, and this led me to jump on one of the "big names" software that offers similar services. After wasting hours trying to set up the campaign, then I remembered Inbox. I logged in, successfully created a newsletter using one of the templates and managed to send it out within an hour. I also got a report later about the click and open rates.
My advice to the developers is to create more updated how-to videos, as I found much of the needed information that resolved my initial struggles from their online written documents.