However, their plates may be lighter than other 5" plates made by others... I believe CMA and 3M are alright and I don't recall anyone complaining about them. Milwaukee is hardly ever mentioned.
I don't think there's a bif diff in backing plates. Meguiar's may have had a QC problem with their supplier but that's fixed easily enough. Beyond that they're pretty much the same except for size. A pro detail shop owner might have a preferred backing plate but that doesn't really apply to enthusiasts who use a polisher only a few times per year.