I can tell you from experience that any new catalytic converter, no matter how cheap, will get a vehicle through emissions testing immediately after installation, unless something else is wrong that causes it to fail. Subsequent years are a different story. I bought a cheap one once, and it only got me through 2 years before I had to put the right one on it. The sooner after installation it is tested, the lower your NOx reading will be. Just drive it on a highway for at least 15 minutes before pulling in to the test facility. Don't add anything to the gas, and don't use premium. My ride failed a tailpipe emissions test once with premium, then a week later with midgrade, then passed a week later on regular, with no repairs or adjustments. If your oil needs to be changed soon, do it before the test.