As with any coolant, you must replace it every 2 years. The reason is any water contact with metal... will create acid... so over a long time... it will start to eat your gaskets... metals.. etc. This is why you see coolant related problems.
Mechanic don't tell you this or even think about it because they want business for repairing big stuff that cost you $$$.
As for MB coolant being superior... that's because I read reports on composition and how they are formulated. The green stuff has qiute alot of silica... it is a necessary component of coolant protection... However, the coolant is set to be alkaline... alkaline is not good for engine either... but okay... Anyway, so as the coolant gets old... it goes from alkaline toward neutral to acidic.
MB coolant is much less silica... which is better for aluminum engine... and the coolant is buffered base... meaning it is formulated at near neutral pH level... the pH remains at that level until it is exhausted and then it goes toward acidic pH.
So technically, MB coolant is superior because it protects the engine by having the pH remains near neutral for far longer time before it is exhausted...
Whereas the green stuff is caustic either way and does not stay at near neutral for long because it is like your fuel gauge... goes from alkaline to acidic as you empty your gas tank.