I reckon the paper oil filter would've caught the ferrous particles really but as you saw in the video, there is still some magnetic material to be caught. I guess it doesn't hurt.
The cylinder walls and piston rings are ferrous, and they're what shed the most particulate matter. The cam shaft and lifters are also ferrous, and those components are the most susceptible to wear caused by fine particulate matter. Magnets can trap particles that would otherwise pass through a typical filter media.
While it's questionable how much magnets help, they certainly don't hurt. They will trap ferrous particulates, (the most damaging kind) that are finer than the filter media will trap. The question is, what percentage are those magnets actually collecting? Many proponents argue, that the magnets at least serve to prolong the life of the filter media, reducing the possibility of bypass, which allows all debris to recirculate through the engine. Not a good thing! If you change oil and filter regularly, this becomes less of a concern.
