Just a note--I've ordered and used EVERY one of those supposed top cleaner products, only to have them do absolutely nothing. I too, was more comfortable putting a dedicated top cleaner on the top to clean, but none of them worked. Tried Raggtop, 303, Amazing Roll Off...nothing.
So, right now, the ONLY thing that works for us (and works beautifully, I might add) with the thick white vinyl is the bleach/water mixture. Has yet to visibly hurt either the vinyl on the Buick or the Caddy, and both are still soft and shiny afterwards when I apply the usual protectant--which has been Mop n' Glow lately.
Actually, as I've been told by a semi expert (who used to sell pool products) after looking at our tops, the problem is mildew, and by using the bleach mixture we aren't really hurting anything per say, but aren't officially getting rid of the problem--the gray/black mildew down below--just making the top look good for a while, then it comes back over time. She actually told me to use a pool liner cleaner for black mildew, but I haven't gotten around to buy any.