Engine coolant and engine oil type, and interval to change them seem to generate the most opinions on this and other auto forums. With or without valid engineering reasons is another topic. I spoke to friends of mine who are on the forefront of engine testing:
Their advise to me:
1.) AL alloy engine/radiator and plastic top tank is a different animal from gray iron engine.. Treat it with respect else you will pay (dearly).

2.) Use the manufacturer premix 50/50 engine coolant.

3.) if you have to mix your own, use distilled water and NOT TAP WATER

4.) Distilled water is only $2-$3 cost vs tapwater, Very cheap insurance policy.

4.) Change coolant per maufacturers' recommendations.

My advise:
perferred method: Use MB 50/50 premix (its only $10-$20/gal)
alternative: Zerex-G05 ($8/gal) +distilled water ($0.70/gal) mixed to 50/50 by volume.

Dont use Dexcool on a MB Al engine.