I've used Souveran, P21S and Natty's.
Souveran and P21S go on and off like warm butter, with temps as low as 50 degrees on cloudy days.
Natty's is a little more difficult to get a thin layer laid down, compared to the other two, more or less the same application conditions.
Natty's gives better sheeting of water than the other two.
Souveran gives a deep wet look.
P21S is not so deep and wet, but seems to give a brighter reflection.
Applied over AIO & SG. P21S x 2, Souveran x 2, then Natty's x1.
Just my personal opinions/experience and your results may vary.