A GameKlip is ok, but having to carry around a Dual Shock or a 360 pad?
This is a lot more portable, not quite as wide as a Galaxy S4, a tad taller though. It's probably significantly more portable than having to carry your phone + a seperate 3DS or Vita too (since no one goes anywhere without their phone anyway).
What I would like to see added to this is a second battery though, it seems like it would be perfect to house a secondary battery since it's just probably empty plastic mostly.