Here is
the Humdinga page on the Gibbs website, including videos. Confusion over the Gibbs amphibians can be caused because they make three different-sized models - but I think the two-seater graphic is just an artistic rendering.
Of course the central steering position means they don't have to make left- and right-hand drive versions - being made in Britain, they would need to make both to please all customers.
Incidentally, driving on one particular side of a vehicle is only habit, not necessity - there is no problem at all to drive on the 'wrong' side of a vehicle, even Americans can do it (though I admit you can see some very worried drivers just outside the rental car depots at London Heathrow airport....).
Andrew