I have been using the Nova based ones and have nothing but good things to say, love the power, runtime, quality and above all ease of tune, Bellgate has also been an amazing distributor and have answered every question ive had and give great support. Im assuming this is pretty much for OS fans and the nova based ones will be for those looking for good engines on a tighter budget, also for what its worth Robert Batlle got 2nd in last years worlds using the M4RZ, so trust me when i say that the nova based ones are no slouch.