I have the folding Walds. 582, I think. I use them both or one at a time according to the load, even though I do have a front basket. The front is just to put some weight up front when both back baskets are loaded. No, interference with any mechanical things (rim brakes, I have no idea about disc).
I have to have them mounted quite far back on the rack to prevent heel strike. As Tractor said, it all depends on the bike. Mine is a MTB frame.
The PedalRoom link in my sig has pictures of the thing loaded.