The wee fine particles that got stopped and are attached to the center perforated steel section of the filter (by the little holes down inside the oil filter) are by definition "particles that got by the filter element" -- how else did they get there?
For $14 less a 15% discount you can do whatever experiments you want to do, or -- having actually done it and having seen the stuff collected on the steel filter can and having had to scrub all the collected crap off the magnet you will know 1) it works and 2) be amazed at how much fine stuff circulates around in your oil all year long.
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People amaze me sometimes -- some folks in motorcycle land are paying over $20
per oil change to get the very very best synthetic oil they can buy, paying $17 for oil plugs with a little magnet on the tip end of it and paying $50 each year to have their used oil studied by an oil lab and get a lab tech report on the wear by-products running around in their oil "to see what's going on in my motor".
Heck folks, buy a gallon of good relatively cheap Rotella synthetic oil (with the tappet and cam chain diesel additives that you do need for our bikes), buy an oil filter each year, slap the magnet on it and put the filter in for a year while you change out that gallon's worth of of oil in several installments.
At the end of the year, pull the magnet off the oil filter, wipe it off (be amazed at all the crap it stopped) and do 'er again next year.
Your yearly cost of excellent internal preventive maintenance will be the same or less as some folks are paying FOR A SINGLE OIL CHANGE ...
And use the $50 bucks you don't pay for the yearly oil analysis to take your wife out to dinner someplace nice .... she'll appreciate it.