Could be Just the perspective but I keep thinking that the rear nacelles are mounted a little to far forward and inward than they should be to make a safe transition to level flight. It looks like there could be a risk that the rotars could strike the fuslage, sponsons or winglets during transition or in level flight.
The rear gun would be completely useless in level flight, unless it had some tight locks on it - mind you there are quite a few Helo's that have to have very restrictive traverse locks on the guns as well (you don't want to shoot down your own bird)
I also think that the rear rotars would have a few problems in level flight due to the airflow and engine exhaust from the forward engines (unless they shutdown the rear pair in level flight.
Still it is an awesome design and a great picture (as always) and gives pleasure to look at it (dispite my pedantic niggles)