I change my oil and filter quite often, more often than needed, but I still like the thought of the magnet giving the extra protection. I have seen a lot of drivers, what ever they drive giving their cars a hard time and all those metal parts must come under some stress, weather it be a V8 or rice burner. Once the metal fillings get into the big ends and mains , lots of $$$$$$$$$$$$$$$$$$$$ out the window.
The price of an old speaker magnet (nothing) compared to a rebuild.