there's only 2 real companies that make true high flow cats that actually reduce emmisions. Random Technology and powercore (good luck finding powercores). they are the only high flow cats to pass obdII emissions checks by the EPA. but they're pricey. so do what you must. i had a magnaflow on my accord with a full cat and resonator. still sounded kind buzzy, but it was much deeper and sounded kinda mean. I now have a full apex'i WSII and it's SOOO much quieter. I did notice with the magnaflow i lost some downlow tq. you gain maybe 1-2hp top end but the loss in low end wasn't worth it for me.