Our catalytic converter was stolen a few months ago. It was strange because we were parked in front of a government building -- library and courthouse -- and were only inside for about 15 minutes, in the afternoon. Came outside and the car sounded like the muffler was missing, or like I was driving an old tank.

Our new car came with installation of a catshield. When talking to various autobody places, they were skeptical it would matter because if they'd cut out the catalytic converter, they could just cut out the shield. It would be nice to see if they had data on this, but I haven't seen any (I even asked our insurance agency if they knew of any analyses on it but they said they didn't).

It is indeed a huge pain in the ass to chop out exhaust components behind anything at all. Cutting tools are all speed and no torque.

If you use stainless or something it will really piss them off. Aluminum will deform, frustrating cutting attempts. Mesh will block access just as easily, maybe go for a stainless mesh so its really annoying to cut through and bank the weight reduction/cooling benefits.

If you use a grinder, the abrasion will take a lot longer as you have to clear both spots where you would like to cut.

If you use a sawzall aka reciprocating saw, the blade has to have totally clear movements or else it will flex and slow down.

If you use a torch it goes quicker, but the set up and hauling the tanks is not easy, torches are fiddly, especially if not properly maintained, the smoke is poison, and theres fuel lines down there to boot.

Unpleasant. They'll just curse and roll onto the next mark.

The thiefs like to be in and out very quickly for obvious reasons. Without the shield it's a couple minutes. If they jack it up and there's a shield, that's going to take 15 minutes, they'll likely just abandon it as the risk/reward isn't there.

A skilled jackman can lift a car in mere seconds. Just watch some NASCAR

Unless you're saying all thieves are NASCAR level skilled jackmans - I don't see how it is not a deterrent. Sure some maybe but if most aren't it still slows them down and adds noise.

Parking in a strategic location (ex: on a hill, etc.) that makes it harder to get under the vehicle or jack it up might help too.

Never thought of that, sounds like a good idea if you live in San Francisco.

I don’t understand how this would prevent someone with an angle grinder from cutting through it anyway. Especially the aluminum ones

Grinding metal makes noise and attracts attention. It's not a solution rather a deterrent to make it harder for the thieves to get to the cat without special tools.

I was debating whether I wanted to add unnecessary holes to the bottom chassis. I wish I had done so.