I have only tried #20, so I can't really comment on how it compares to Klasse objectively, but several members here have told me that Klasse has better shine than #20. As for NuFinish, I have smelled it and know people who have used it, and as far as my opinion is concerned, it has much better cleaners than #20; therefore, it is much harsher on your paint.
Why not #20? I find it easy to buy locally, and easy to apply. And if the prep is good, the shine is outstanding. Maybe not as good as Klasse or Zaino, but certainly makes me very happy.:up