I haven't used Zymol, so I don't know how it compares. P21S is actually formulated in Germany, I think. It's advertised in some of the high end car mags, like Excellence and Corvette. You'll also see that outfit's wheel cleaning kits advertised from time to time. However, I haven't seen it much on the shelves at car parts houses. I got mine off the internet---www.performanceproducts.com, along with what it calls a "paintwork cleaning lotion." Ooooh, love those marketing terms. Anyway, it was the only natural wax to score a B+ overall in the guru reports test of 46 waxes and polishes. Zaino (a
synthetic), of course, got an A-, even higher. Zaino has a product labeled Z5, which is the polish prescribed to help hide swirl marks, etc. I just found that P21S did a better job of that on my black Z06. If you want to get serious about actually polish out most swirl marks, etc., neither of these products will actually remove the marks. As a general rule, I don't like to cut the paint with abrasives, so I'm willing to live with some swirl marks in black paint, the hardest color to keep looking good, IMHO. Anyway, good luck.
TT