Mine wouldn't polish a tomato.
Basically I think they are used as a buffer. Put the polish or T cut on by hand, and then take it of with one of the mops, and buff it to a high shine with the other mop.
They call it detailing these days. Loads about it on the interweb. If you really want to make it look horny, clay bar it first. Clay bars are the kit, but halfords seem to think they are gold bars, the price they want for them. cheaper off the web.
Mequiars (sp?) polish, showroom finish, seems to be raved about. Got a bottle, but havent tryed it yet.
Doesn't matter how good the polish is, its the prep with T cut and claybar that makes the difference. Takes a lot longer to do a van than a car though. I find it daunting.