I'm sorry I mis typed.
Whatever the magnet picks up is too big to be read in UOA, magnets do not affect UOA. Anything the magnet gets would get picked up by the filter. The only thing the magnet does is keep the filter clean of that debris.
This has been beaten to death here.
I still use one, but I never get the amazing pictures that I've seen. At best, I get a stain that won't wipe off.