The biggest advantage of the "stronger" magnets I can think of is how well they cling to the frame/toolbox/metal workbench so they don't fall on the floor and roll under stuff. I hate when that happens.
Since the primary doesn't have a filter, and the late model compensator sheds metal like a dog sheds hair, perhaps that one would be a good idea. As for the engine, I don't see a whole lot of advantage. First, the oil in the pan on a Twin Cam goes to the filter first before it goes to the engine, so anything of significant size will be filtered out, including the nonmagnetic aluminum and plastic particles those magnets don't catch. Second, none of these peddlers of magnets, be they on drain plugs or in/on an oil filter, provide certified independent test results proving the products actually reduce the amount of metal in the used oil. This is something you can determine easily with a simple used oil analysis btw, if you're really that worried about junk in the oil.
Bottom line with this as well as a ton of other products being hawked these days is that the benefits are usually overstated and the price inflated. If this sort of thing makes you feel better so you can sleep at night instead of worrying about your Harley self destructing every time you fire it up, and the price won't put you in the poor house, go for it.
Jerry