I have a mazda mx6 that had a bad cat. The cat I had put on it was $80. That's much better then spending triple the cost on one cat alone. I'll bet that the cats are no different save for the fact they cost more. One problem with aftermarket cats is the logic in the ECU that is used to monitor the efficiency of the catalyst is based off the catalyst that the car was produced with at the factory, and I've seen cars with relatively new aftermarket cats come in with a P0420 (catalyst efficiency below threshold). Not saying it will always happen but I've seen it more than once. (I'm a Subaru/Toyota technician) I don't know how they do the smog tests in California, but up here in Oregon if it's 96 or newer most of the time they do an underhood and sometimes an under car inspection, looking for missing cats, non street legal carburetors, etc... Once that is done they will check to see if the check engine light is on, as well as make sure that it comes on when you turn the key on, but shuts off once it's started (to make sure it hasn't been removed) and then they are supposed to plug a code reader in and make sure there are no codes in the system but they don't always do this. Cars that still have an on board computer, but are not OBD2 compliant (pre-96) will usually have an underhood inspection and a light check, and sometimes an exhaust analysis but at some of the shops this just consists of them putting a 5 gas analyzer in the tailpipe and checking the emissions at idle and at 2500 RPM. (not under load) Now don't think that you can just clear your codes right before the smog check and hope they don't do an exhaust analysis. The reason for this is the way codes are stored and such. When you are driving your car, the computer is always running component checks. Some of these, such as the misfire monitor, are continuous monitors, meaning the computer is always checking them. If you unplug a spark plug wire on your car, it will throw a code almost immediately. Same goes with most of your sensors, the circuit check portion of the monitor is continuous - if you unplug your oxygen sensor, it will throw a code immediately. Other monitors, such as the evaporative emission control monitor, and the catalyst monitor, only run under certain conditions. These monitors will set a code if a failure is detected, but will only turn on the check engine light on the second failure. Once a code is set, it takes a certain number of trips without a failure to turn the light back off, and I think it takes 40 for the code to go away. It's also stored in the computer which monitors have run, and whether they have passed or failed, and most newer cars will also record the total time since the codes were cleared, so if you go in to the smog check station and your light is off, but none of the monitors have run, and it's been 180 seconds since your codes were cleared, it's going to be an immediate red flag and they'll either tell you to come back later, or run an exhaust test. There are three types of codes, pending, history, and current. Pending codes mean that the monitor has failed, but it's the first time for the failure, and the light is not on. Current codes mean it failed this trip, and a previous trip, and the light is on. History codes mean that the last certain number of trips (varies by code) the monitor passed, but sometime in the last 40 trips the code occured. There is actually a fourth code type, the permanent code, I don't know if this is an all-inclusive, all manufacturer thing, or if it's just Toyota, but certain malfunctions will set a "permanent" code, which will not clear even when clearing the memory with the scan tool. The only way to clear one is to repair the problem and perform a drive cycle, once the cycle is complete and the monitor has run and passed, the code will clear. I hope this wasn't too long winded for you guys!