Kout doesn't really seem to be launched (you can only sign up for list). Whereas Gumroad lets you sign-up right now.

Gumroad's design is also a bit more inviting.

I hadn't heard of either of them until today, but one is definitely in a place where I would share the link with buddies, and the other I wouldn't.

You ask about "buzz" and I definitely think launching a working product is more newsworthy than a beta sign-up page. That said, Kout seems interesting as an idea.