i was just looking at the junk on ebay when i noticed that there was a hi flow cat that is actually legal for 70 bucks

http://cgi.ebay.com/ebaymotors/ws/eB...category=42610

are these things worth it? are hi flow cats in general worth it?
or should i just buy one of the stainless steel 40 dollar ones, or not buy one at all?