I have all 3 and each has its own personality and usefullness -
All L/C backing plates are designed like this picture - not much flexibility, but since its thinner, it can allow you to get the pad edge up close under things sometimes, like mirrors, etc..
Flex-Foam - great backing plate, more flexible sideways and down, but fat on top and not as easy to get under things.
Meguiars - great plate, flexible also but also fat on top and not as easy to get under things..
Everyone is talking about and probably using the flex foam plates which are a lot like the UK/European 3M version that can be bought some places in the US for around $70, and while they are good and certainly act and feel differently, It makes me wonder how much rotation is being lost as the plate may flex sideways as well as down, etc.. Probably not much, but I always wonder because I am a Detail freak I guess....

Dan F