How often to demagnetize mc cartridges?

Never it does not need it its a scam.

I try to demag every 50 hours of play. The Cardas album deflux treatment is also one of my protocols. Enjoy the music

Depends on how the coils are constructed. If iron core, the core can be magnetized. Then an occasional hit with flux buster is worth doing. But not very often.

OP is this similar to what you got?
https://www.audioasylumtrader.com/ca/listing/Accessory/Aesthetix-Benz-MC/Demagnetizer/206532

@lewm , would you say that I need to rethink my protocol as stated above? My cartridges I am using in rotation are the DRTxv1s, ZYX original copper Universe, Shelter 901, Koetsu RSP, AT ART9 and ART7 and a Grace F9 SS optimum line contact, the latter MM I do not demag. I have followed this protocol with no derogatory results, that I can tell, but wonder if what I don't know might be hurting me in this matter. Looking forward to your response, not trying to bait you on this, do believe that it is pertinent to the OP. Thanks