Different strokes for different folks........I've heard plenty of K1's and they sound utterly hideous.......but only for my taste others love it.
We've seen welds rotting, fitment nightmares, baffles rattling (i think). Basically it's a case of you get what you pay for.......some break lucky.....others don't.
It's not about having your head up your arse.......Japspeed very specifically are one of the lowest quality brands available for the zed. That's a fact........however they're also one of the cheapest.
Do it nice or blow up mice! ;-)