I have them in both my bikes and there is something on them every time I drain the oils so I do not think that they are a waste of money; besides anything the makes you feel warm and fuzzy about your bike is money well spent in my book. Given that I rolled my own with .25" x .50" Rare Earth Magnets that I drilled and pressed into my stock plugs; I can pick up at least a 16" adjustable wrench with them.
Dayum!! No need to wonder why your credit cards won't work for you all the time, Tony!
All these strong magnets are going to keep your reciprocating parts from moving...