Not sure how much ferrous metal there is on my n52 engine, however on the last oil change I did fit a comparable product: https://www.opieoils.co.uk/p-83815-gold-plug-ap11-magnetic-oil-drain-sump-plug-for-bmw-vehicles-ap-11.aspx
Not yet done an oil change since fitting, so no idea if worthwhile.
I can say that these type of magnets are incredibly powerful (for their size). On my previous Toyota it did pick up some small particles..