Hi,
Oilled performance filters, only contaminate the MAF if they are not maintained properly, over oiled and/or oiled on the wrong side of the filter, I have used K&Ns and BMC filters for well over 200k miles now on my Audi, and my Mercs with only one MAF issue this occurred within a few hundred miles of fitting the filter, replaced it and have had no reoccurrence that was over 100k miles ago now.
Regarding performance economy improvements, C230K improved the MPG slightly, performance negligible, C43 AMG (55 AMG Engine fitted) no discernible economy improvement, performance it did seem to make an improvement but not sure whether this is just a placebo effect, as the filters give it a real throaty induction noise through the twin cold air intakes. My Audi 3.0TDI Cab, I have noticed neither performance or economy improvement.
I only fitted the filters in the first place to eliminate the expense of OEM filter replacement, the AMG filters for example are £117 to replace as opposed to £60 once only for the K&Ns.