I wouldn't use that...
The porcelain on a kettle is basically glass. It's not paint. What might be safe for paint may not be safe for glass (porcelain). If it says "safe for use on glass" then I'd test it inside the lid to see if it does anything. Any product that improves the shine of paint probably has a polishing compound in it that "could" scratch your kettle.
Having said that, there really isn't much you can do to improve the shine of glass (porcelain) in my opinion. If it has scratches in it, you're really kind of left with them. Porcelain is very hard which is why steel wool doesn't damage it when we use it to clean these kettles.
Sorry, not trying to be a wet-blanket, just don't want to see someone ruin a perfectly good kettle. Hope this helps..