I've not heard of it at all, but I'm not a iThing sort of person, so it's understandable.
Obviously, you'd need to check "allow non-Google installs" in settings, to get the additional content from the Box, unless they are only making a wrapper around the google play store? I don't see how that would work, without checking that "allow" setting.
It's interesting, I guess-- but I see little need for re-inventing the play store, for a limited set of apps. On the other hand, having a set of apps that are tightly integrated with each other could make for an easier time of it, for some people.
Interesting idea, though. I wonder if their pricing will be competitive with other 3rd party markets, such as Amazon's?