Placebo, snake oil, waste of money, take your pick... car/engine manufacturers and the oil industry spend billions developing engines, oils, detergent/additive packages. If any of these oil treatments were as good as they claimed why aren't they used by or recommended by the companies that design and manufacture* engines etc? When was the last time you heard about an regular road engine physically wearing out without having done galactic mileages? Far more common is some ancillary bit (often emissions based tat) failing that either had nothing to do with the engine oil or as a result of repeatedly skipping services
Any oil that meets whatever MB spec (229.xx) your car needs is fine. Dunno if the Castrol Magnatec ticks that box but, generalising, Castrol (and Mobil) are overpriced 'meh', the name is worth extra to some people and someone has to pay for all the advertising...
Something like Fuchs (used to be factory fill on many MBs not that means much beyond MB finding it good value/getting a good rate) is usually better value although a large part of that may be because you don't find it on the shelves in Hellfrauds or Eurocraparts etc. FWIW i usually feed my s124 Fuchs (229.1 in my case), dunno about it's life before i bought it but it's currently on 214k (bought at 178k) and uses so little oil it rarely needs topping up between yearly changes. Never poured any snake oil in the engine or the fuel tank, i use supermarket fuel and when i MOT'd it this morning it recorded 0.000% CO initially before sailing through the emissions on it's origional 22 year old cat. All i do is service it by the book and give it a good caning regularly
Marketing = BS. Always and without exception
* before anyone shouts because the manufacturers want the engine to wear out so you buy a new car remember that extended service intervals are the thing these days (appeal to fleet buyers/'renters'). Anything that would let them extend service intervals further would be seen as a good thing by them. Car manufacturers don't sell cars anymore, they sell finance...
