The JWT Popcharger is a cheaper version of the Stillen Popcharger. The only difference is in the heat shield...the filters are the same. (They are made of cotton, just like the K&N) In fact, you can clean and re-oil with the K&N filtercharger kit! The K&N is a drop-in filter and will not give you the extra sound of the popcharger filter.
Personally, I prefer the look of the Stillen...but the performance is the same. The Z-tube should be used with both.
http://www.g35parts.com/9083/o...58_21