I suggest the safest policy is to follow the directions in the owners manual verbatim.
I doubt Mercedes does any break in during the manufacturing process. Two reasons:
1. It would not be cost effective in their process to do so. No bang for the buck or Euro.
2. If they did, why would they bother then to recommend an owner break in?
Breaking in at the factory would require putting each engine on a dynometer which would be hugely expensive. While some very low production/high cost engines do get treated this way, I doubt any higher volume manufacturer could justify it.
I saw some drive testing at the factory in Sindelfingen, but it was over a few hundred yards, not miles. They do that just as one final check before loading them up and not as any kind of break in. I'm also not sure if they do it for all models.
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