[cmiovino]

I've used a handful of various magnetic plugs on my WRX and BRZ. I will caution you against any cheap aftermarket plugs - especially with a magnet protruding far out into the oil a 1/2 or so. I've had one of these chunk off a piece and end up in the engine, filter, etc. Didn't do damage fortunately. It was a "Blox" brand, which isn't exactly a no-name eBay one either.

Subaru makes an OEM magnetic one that worked for my WRX. OEM and was a flat magnet. I run a Dimple brand magnet one that's essentially the same thing for my BRZ. Only real reason I changed it was the previous owner managed to start rounding off the OEM one.

I have seen some minor debris/buildup on it since installing. Like a silver metallic goo. It's common if you run a magnet. These very fine particles would likely be picked up in the filter eventually. It's kind of overkill.

I personally don't run a Fumoto valve because I autocross a lot. I could see it getting caught on a cone potentially under the car, even with the stock shielding under there. Maybe. Unlikely, but it's one less thing to worry about.