From my basic understanding, the NMotion will give you great bottom and mid power but wont do all that well up on top. Basically a MX type of pipe. The only downside of the NMotion will be the noise, coming in at a tad over 110DB which is retartidely loud. So unless you plan on doing MX for the most part then go for the NMoition I really haven't heard any bad things about them. If you are looking for an all around great pipe get the Yoshimura, I have the TRS Carbon/Ti full system on my Raptor 660 and I love it.... Not to loud, excellent power gains and not to mention it is IMO the best looking pipe out there. If you want an awesome pipe, reasonably priced and I am almost certain that this pipe is the highest HP producing pipe for the Honda 450R get a Rossier. They look cool and there not too loud.
Check it out.
http://www.rossiereng.com/atv.html