I've used to polish some parts of my car with a grinder, and never had any issue with that, the only problem was that when I first bought my first grinder I didn't know any details about it, so I bought a medium one. The only bad thing was that it was heating too fast, so I had to wait some minutes to cool. In my opinion instead of constantly buying those kits that you might lose somewhere in the garage, you can polish the exhaust with any doubt with a grinder, and if you want to buy one I can recommend you this article
10 Best Angle Grinders, it helped me into choosing the Metabo WEV15-125, great one.