Hmm.. thats odd, since Mercedes OEM spark plugs costs $10 canadian each (same price as bosch platinum +4) .. $2 US = $3 canadian sounds like a great deal.. but I believe non-platinum spark plugs have shorter lifespans than plantinum plugs.. so you will actually be changing them more often(more chances of not installing them properly), you have to remember the car is heavy and the engine needs to work alot to get it moving... can those regular spark plugs take the load? btw: you will need 12 spark plugs for your ML.. not sure about your c-class. For the price I believe your spark plugs only have 1 gap, whereas the #4418 have 4 gaps...