It looks like the only tracking is open rate? Now I don't enjoy being tracked myself, but sadly it's a fact of life in email marketing, and table stakes for email products – is there any click through rate tracking? How do you handle custom click through domains? How do you handle anti-tracking technology in Safari? How do you handle open rate tracking with Gmail and other clients pre-loading images?
A common request from marketing (name may vary) at my previous company was for all emails to be sent at a specified time. Do you handle this? If not what's your send-rate per customer, how long should customers budget for a campaign to go out? What's the quota per customer on the send API, how many requests per second can they make?
A common request from engineering at my previous company was for emails to be spread over a time range so that the site didn't receive a million hits at once, even just hits loading dynamic images from the emails, let alone actual click-throughs. Do you have any controls for spreading delivery over time?
How do you ensure your users are GDPR compliant? The example email on the homepage doesn't show an unsubscribe link, but these are legally required in many countries. How does the tooling support this? Do you offer end-users one-click unsubscriptions? Are users prompted when they attempt to save a template without an unsubscribe link to prevent human error?
Having developed a few HTML emails in my time, this does look like a joy to use for that purpose, but having seen a company try out different transactional and marketing email service providers, overhaul their email approach for deliverability, cope with the Safari tracking changes, keep a site online during sale periods, meet regulatory compliance both for the company and for our clients, and accidentally DDoS itself with emails multiple times in different ways, I'm not sure Mailhub solves or aids any of these problems.
In the end we mostly either outsourced the HTML email authoring for little money or used frameworks like MJML, and the HTML email "tears" went away.
If you have solutions to these problems, great! I'd highly encourage you to add them to your marketing page or docs (I couldn't see them) because these are things potential customers may be looking for. If you don't have solutions I'd encourage considering them.