MC cartridges and metal platters


I have read you should not use a MC cartridge with a turntable which has a metal platter, and Music Hall strongly recommends not to do so, at least on their Music Hall 2.2. However, every single HIFI dealer I have talked to disagrees and state they have done this countless times without problems. What is the truth?. 
boofer
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Thanks again, Viridian; looks like my restored TD 150 and 160 Super pass the  nonpermeability test, and I can continue interchanging my 4 LOMC cartridges between them.   

czarivey: I looked up  QRK   turntables, found it quite interesting. Thanks for your input.