If magnetic drain plugs do no harm, then there can be no legitimate argument against using them if a person has the money to afford them and wants them. JMHO
I see the magnetic plugs as more of an indication of whether metal is being picked up by your engine oil. I don’t believe the plugs attract every piece of metal. The magnetic field isn’t that strong. They provide you with a visual sign that something is going on when you pull them at oil change time. Otherwise you would have to cut into your filter to have a look.Magnetic drain plugs are found on just about every gas-turbine or jet-engine, including turbo-props as well. I flew mostly turbo-props for thirty years and had one catastrophic engine failure. The front bearing let go in flight, a slight unusual noise, a buzz, then we focused on the oil pressure which slowly began to fall. We reduced the engine to idle and just landed using the other engine. No big deal.
Our mechanic removed the engine oil drain plug which was a magnetic plug. There was so many metal filings that the filings filled have of the oil sample jar. No magnetic plug required here. A magnetic plug will detect trends in internal engine problems. I will not bother to fit my S-Ten with mag-plugs because I have great faith in Japanese engineering and machining. Just my 2 cents worth...