Superhuman paying customer here. For starters, they are not equivalent products because Hey.com is client + server. Superhuman is an app that sits on top of an existing Gmail account.

I have no problem paying for Superhuman. I use it exclusively for my business email and the way I see it, if improving my email management lands me one single customer it more than pays for itself.

As far as paying in general, I enjoy the feeling that this product won't die off in the same way so many clients have before. Hopefully they are able to build a sustainable business and support a reliable product. Superhuman also has outstanding customer support.