I don't know if this was clear from the homepage but we're targeting site owners. Many sites use mailto links because they don't want to go through the hassle of setting up a contact form. We're just trying to make that easier to do.
Edit: Thanks for the feedback. We can absolutely show the actual email address and even include a real mailto link inside the widget incase the users prefer that. We'll be implementing that right away.
The customers of site owners (OP) are saying that they'd prefer if the site owners not implement this form.
I think that you're argument about how the mailto link is bad, is bad. You could argue that a mailto link should be added in addition to your product. The classic example is to have the email address lit up with a mailto link and a form just below it.
Feature request: Don't hide the email address in the link, so I can right-click copy it, and add a small "email us with your email client" link at the bottom with an actual mailto. This way, we get the best of both worlds.