As for the diffuser, having the exhaust exit on the other side of the car is a better flowing layout and what I've done on mine, it allows a full diffuser to be fitted...full diffuser is also being developed
I never really understood why Nissan did the exhaust out the drivers side, it makes much more sense coming out on the passenger side, I did this on my last pulsar as well.
I'll only agree with this if you want a big standard type silencer under the boot floor. Otherwise I don't see how the mongoose idea of over the back axle and straight out is inferior to putting at least another 2 bends and 4 or 5 feet of exhaust pipe in to allow it to come out of the other side.