You don't have to buy the more expensive Mercedes-Benz original parts. You can get identical FAG or Timken bearings at any auto parts store for less money. In fact the blue Mercedes-Benz parts boxes contain either FAG or Timken bearings. The part numbers are in the image below.
If you have a choice - get the FAG bearings. They last longer and fail less often. Timken bearings vary in quality depending which of the many factories worldwide produced them - Timken France bearings are the worst.
If you get MB original parts check what's inside the box while you are at the dealer. Refuse when they have Timken France bearings inside -give the guy a tip if the box contains FAG.