The chambers are stacked in an attempt to save length and keep the thing easier to manage.
It looks like it would be awkward to shoot. Though it is somewhat interesting.
Wouldn't one chamber be easier to manage? It would save having to buy an elbow as well as an end cap, and it would be alot easier to pinpoint any problems you may come across with the chamber(s).
And I think i can recall JSR stating that the optimum chamber to barrel ratio is 1:1, without the second chamber you would be almost spot on.