Yeah, if you want to have an immobilizer circuit, immobilizing the button won't do much. Cutting the button after the car is stolen won't do much if the car is on and driving when you immobilize it. You want to immobilize stuff like the fuel pump, ECU, ignition system etc. You also want to hide the module somewhere that's not under the steering column (I took my dashboard out in one of my cars and put it behind there). Not sure how these products wire in their remote "turn-off" (like actually turning the car off instead of a cut) features though.
Having said that, largely the only way to steal these cars from the factory (excluding tilt trays) is to take the keys. So if you're using one of the systems that has a key fob type tracker like some Viper systems so that you use to immobilize and they keys get stolen, then there's not much to do. Phone app ones look okay tho, but still the best thing to do is to not lose track of the keys.
