The car is indeed picky (or at least its engineers were) but the stuff you have meets the spec.

You should never use generic coolant. Zerex G05 also meets the MB spec.

The stuff you have is, I believe, full strength. So you should mix it with distilled water.

More importantly, you need to find your leak.

A common point would be the weep hole for the water pump, which is mostly hidden behind the pulley. Take a quick look with a flashlight from above, if it's not evident spend the time necessary to pull the belly pan (it's not that bad, and that way you can dump all the accumulated sand, dirt and leaves out of it, too). Then you can look up from the bottom and have a better angle on it.

If there is absolutely zero evidence behind the pulley (even no dried "tracks") then check the windshield fluid container. Engine coolant is cycled through a coil in it and the hose connections can develop leaks.

But needing coolant is not normal, so be sure to follow up. And that way you don't need to worry about whether what you have is okay to dump in between changes.

Good luck.