As disclosure i have used multiple email campaign engines, currently i am using Mailwizz.
Feedback
Checked your demo page product looks legit. seems lightweight and is fast, has smooth navigation, must have options are in place.
Assumption
Could be competition issue, there are lots of quality product on the market that already solve the same issue and have much more functionality.
Suggestion
Hoverer there are some issues that current products do not support, and could be game changer for your product.
Top issue is quality page builder for landing pages and emails, there are lots of opensource libraries that you could easily use GrapeJS would be a good start!
p.s.
My product is much simpler but unique in it’s field, if you have experience with perfex would be nice to have your feedback on it.