I bought one of these at New York Comic-Con this weekend — it's a surprisingly good facsimile of an old NES cart; and the rubber stopper (rated to 10psi) performs better than it looks like it would. My only complaint is that it's a bit awkward to nip from directly, though it'd be fine with a straw.
They've got five parodical "titles" to choose from (I got "Drunk Hunt"):
Super Bar-Hop Bros.,
Metal Beer, and
Legend of Drink.
The hardest thing about creating a concealable flask was where to put the cap. I think everyone on the Ink Whiskey team could attest to that. Eventually my plastics engineer and I spent an evening at a bar designing flask caps on napkins until we came up with the minimalist design that we currently have.
This cap replaces the grip portion of the cartridge. It was the only place on the whole design that had natural shadows and indents that wouldn't be noticeable by change in design. It was the perfect location.
You'll notice that the actual plug portion is just slightly larger than the grip section of the cartridge. This was so we could have a larger spout for the flask, which then provides an easier pour for its contents. If you look hard, you can see the slight rounding at the base of the cap, but that's the Ink Whiskey Entertainment Flask's only give away.