There are reasons why a manufacturer of a class and reputation of a Mercedes recomends certain products. They are made for their vehicles and ensure long life.
Here's a link that everyone should read.

http://www.mbca.org/pages/tech/MBCA_Antifreeze.htm

You can use plain water in you car also, and that will work. Over time however this will do harm to your engine. Same with wrong antifreeze. You might not even know that you are harming your engine. The car might run fine for 200,000 miles and you will think that's great. What you will never know is whether the car would have run for another 50K or 100K or whatever miles.

Same goes for oil. I use Amsoil - European Car specifications, even though regular Mobil 1 is most likely just fine. It's only $20 bucks more per change, and that is not cheap enough for a piece of mind.
I have nothing against doing the work yourself, but if you're going to cheap out on parts then you might as well buy a Kia.