I just had to make this decision for my kids Camaro.
There are the super cheap ones on Amazon, I don't put much faith into them actually doing much at all to scrub the exhaust.
I spent some time looking over the interwebs and ended up spending $126 on a Magnaflow that is robust and has a much thicker core than the cheapies on the Amazon.
I also noticed that the Magnaflow I picked had a "EPA Compliant" rating on it.
I took that as meaning it would actually perform a service other than making it so that I could pass a visual inspection...
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The center of the cat body is the actual width of the material, unlike the ones online that are supa cheap.
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Now, I haven't completed the exhaust yet so I have yet to see if it actually works and passes the DEQ sniffer test.
This is just my recent experience with having to purchase a fresh cat for a car.
You may have a totally different experience than mine.