Are aftermarket catalytic converters any good..?”
I don’t know what you mean by “aftermarket”. Most pollution control equipment has to meet stringent specs. Since many states have yearly pollution testing, any notably bad replacement cats should have been weeded out by now. I suspect since it’s a relatively hi-tech device, with ceramic inserts and palladium and other metal catalysts, these are unlikely to be made in some mom-and-pop shop, more likely made by the same companies that make the OEM ones, and rebranded.
