Local Shop Mufflers

hey guys, anybody tell me the goods and bads of local shop mufflers?

or lesser brand names, like 3A Racing, X-Force, or MagnaFlow?

i figure, after going into an exhuast shop, that theres no point in getting the piping and muffler if i cant change the CAT, and that if for jsut looks, then the muffler is fine. so if its jsut for looks, and *note*, then is it alrgiht to get any ole cannon exhaust?

thanks