[Rich in Vancouver]

OEM implies that the parts were made by the original supplier and in theory the quality should be the same. Keep in mind that most MGR parts for sale today were made long after they went bust. (Particularly fast moving parts like front lower arms) With parts like this it is likely that the only difference between the originals and the OEM is the lack of a box.
Mind you, I recently bought and installed an OEM timing belt tensioner and shortly after replaced it with an MGR unit. The parts were identical with the exception that the OEM part did not include instructions. In that case it did make a difference!