This is also called mild steel.
If not welded properly welds will crack over time. It also requires heat coating on the outside.
Stainless is the best if its designed correctly since it can change shape from heat during welding. They do not need heat coating and in fact if coated can trap heat in welds and cause them to crash.
Best case is a header that maintains the O2s at the proper distance as GM placed them so that they report correctly.
Many header designs shove O2s 12 to 18 inches further back and over time the O2s report incorrectly causing AFR to be off and also can cause CATs to fuse internally.
Vendor I would suggest since they have made headers for cars like the Corvettes for many years and are a direct drop in install
Their website is
http://www.stainlessworks.net/cart/index.php
