This would be muder to your shoulders, where all the weight is being carried. The seat is also a solid construction so it would not move with you as your hips pivoted to walk, creating a gouging sandpaper effect that would chafe your upper back/hip area raw. You would also have to lean forward to balance the weight of the second person, destroying your lower spine and knees in the process. It's more of a torture device than a means of conveyance.
Look at that last picture. That guy is sitting there like a rag doll..... It's just awkward to look at O_O