FWIW, I have 2, one for each of my 240s --- IPD Mag Drain Plug... bought in the 1980s. Never had a problem, the head-nut is larger than the stock NonMag plug, and that was a selling point then for IPD in their catalogue, that came in the mail, plus a monthly newsletter. That was BTI --- Before The Internet

The Magnetic Drain plug,does give you an idea of what's going on inside the engine . When you change Your Own Oil, you'll have to wipe off the magnet and you can eyeball the gunk---(use a paper towel). This way you'll be able to see if anything has changed - oil change to oil change over a long period of time.

Then as the models of Volvo expanded and DYIers got fewer - the 850 FWD years. IPD started marketing all sorts of Magnetic devices, all with nice little paragraphs and pics and graphs showing the benefits.

I saw it as less part sales and more stuff-for-your-Volvo sales. Gottta keep the lights on.

So that said, having a Magnetic Oil Drain plug is a good idea.

Manual trans come stock with magnets in the Drain and the Fill plug...so does the Differential.