I've been using Superhuman for a couple months on and off and I agree that Superhuman visually looks similar to some electron based email clients. However, functionality wise it's quite unique. There is a very strong emphasis on keyboard shortcuts. I never have to use my mouse, which as a frequent vim user is a big plus.

The only issue I have with Superhuman right now is that there isn't 100% feature parity with Gmail yet; however, that's quickly improving with each release.

Disclaimer: I'm friends with an employee at Superhuman.