I just checked that I bought the Keihans in 1996 and the SS headers in 1998. Since I've made about 100 000 km on them, melted a couple of plastic bags on them. Once cleaned, they look and sound like new.
I can't speak for Staintune, but IMHO the Keyhan are the way to go if you can afford them.
(when I bought them, I was changing one Zeuna OEM per year, odd one, the right side, and the other side every other year... So the price seemed right then)