The problem with Platinum plugs(even non-resistor ones)is the size of the center electrode. Back in the days when "Platinum" plugs were $18+ each, things were different.The original platinum plugs were for some models of Porsches and worked very well. When Bosch went to the "Mass-Market" platinum plugs and tried to keep the cost under $5 each the plugs ended up having an electrode that was a very small diameter. Its hard to start a fire with a tiny spark.Same thing with the new +4 Platinum plugs, small center electrode. I'm sure they work well in some cars...just not a Mercedes.
ASE Master Tech
Mercedes Tech 19 Years