I USED to use green coolant in my 560sel until I read an article from Mercedes about the use of their coolant. Using their coolant there is no a recommended change interval for the coolant hoses on the car - according to the article hoses should last up to 15 years no problem. Then there were the numerous threads about the necks breaking off on the rads from the deterioration of the plastic from the green coolant - still I did nothing. Then my rad neck broke and I had to change my hoses - they were swelling. I flushed the system and changed the rad, water pump and all hoses and am Mercedes coolant only from now on. Specialized antifreeze for German cars is not unique to Mercedes. VW has three different antifreezes and it depends on the year of car you own as to which one you use - failure to use the right one will result in premature cooling system breakdown - is it worth the slight extra cost for the right stuff not to use it???? Mixing two antifreezes changes the chemical balance and the PH level - unless you are a chemist - who knows what will result - after my experience I would never do it. I carry a jug of premixed Mercedes antifreeze in the trunk - just in case I need a top up.
When you think about it - why would you use green stuff just because it is antifreeze - would you use an oil in your engine that was not formulated for your engine eg- 30 weight non detergent - just because it was oil? Think about it.