Depends on how they're made and attached. Something that just surrounds the cat and made of hardware store rebar? Not that effective but still a deterrent. Now if the cage itself is attached to the cat at a bunch of points, then attached to the car at an equal number of points, that can be pretty effective. Even better if it's made from something other than hardware store rebar.

Best bet is a literal box around the cat made of sheet steel, the thicker the better. They're likely using a sawzall, which will take multiple blades and a significant amount of time to get the cat out.