I've been using #20 for about 4 years now. Excellent for white and light colours. Light cleaning ability does not allow layering, so I no longer use it for my personal cars except for the wheels. I use AIO/SG on my own cars, but for clients who want a one-step, #20 is quick and easy to use. Durability seems to be around 2 - 3 months if not garaged, that's the other reason I use Klasse also.
Advantage of #20 is that since it's in the Meguiar's system, it's compatible with their polishes and glazes, so you can use Hand Polish or #7 under it if you like, with no bonding problems.