Crikey theres loads of clay stuff in this forum now, I'v only ever used autoglym as I bought it as a one off but I liked it so thats what I stuck with, so I can't really say for other products. The car needs to be wet (not rainwater though, a light soapy solutuion of detailing spray/lube which you can get when you buy a kit), I did mine when it was really sunny and warnm and buffing was a workout so the best weather I would say is dry but not to hot, like if your going to do it in the summer, do it once its cooled a little. Hope this helps you.