I have them on my machine, my fathers machine and have installed them on at least 10 razrs. I like the muzzy because its a little better on the ear drums. DOnt get me wrong... i like noise. We ride at the oregon coast, and all over mountains around my house. Also hit the track as much as possible. The muzzy is a nice clean fit. I think over the past few years muzzy has made huge strides in the offroad world. their fit and finish has been very clean since the first kit installed. I think Rangerdale has a good point though, but i also know how my razr ran before and after and have to go with the real world experience i have with their product.
Or you could skip that step and throw an aerocharger turbo kit on it.....?