I use a Filtermag on my van and have cut two filters open to see for myself. Doing this proved that the pictures on the website that show fine ferrous particles, are for real. I had the same thing, lots of fines that the filter cannot catch.
The particles were still stuck to the inside of the filter casing even after removing the magnet since the strong rare-earth magnets will magnetize the casing i guess....you can buy rare-earth magnets individually on the web but i like the ease of the Filtermag product, to me, its a no-brainer.
If you wanna do it, DO IT!