I like clay and yes it works but in addition try Ironx CarPro Iron X 500ml (16 oz) before you clay as it took lots of stuff off a 2 week old cat. I think it was rail dust as I thought the car was clean but you spray this stuff on and in a few min you see micro rust partical apear to bleed down the side of the car. I like it on wheels as well as it cuts the dust. Only drawback is it is one of the most stinky things I have ever experienced. It is so bad that the sponge I used with it even after rinse can not stay in the garage 3 weeks after use. Anything that smells that bad must work!Clay bar works for removing stuff on the surface,like overspray or things on the top of the paint film.
clay is a MUST IMO!