Technically, virtually all aftermarket pipes are illegal for street use under federal (EPA) statutes in the US, but only a few localities choose to enforce the federal law. If the pipes don't have an EPA stamp embossed on them they are not really legal.
Right No smog or annual inspections in Calif. for motorcycles & we do have decible laws & I don't know any after market pipe stamped legal for street use here ( maybe there are some I don't know of) but the only riders getting written up for loud pipes in my city I know of are Sport bikes, No Harley Riders I heard of. Been riding a 2001 Softail with Samson Big Guns with no baffels for years & never been stopped & I've had numerous cops ride beside me & check out my bike only to give me a thumbs up & ride on. My Sportster 72 has Screaming eagle slip ons with baffels removed & DKCustom TTI. Loud as Hell & the cops just check it out wave, smile, give me a thumbs up, but no tickets. Maybe I'm just lucky or live a charmed life. I say go for it just keep the stock ones if your not as lucky & have to switch back to get a fix it ticket signed off. It also depends on what part of Calif you live in and how you ride & how you treat the officer stopping you I think