I see Flex-A-Lite and a few other companies offer a range of different zinc anodes for the cooling system, the two must popular types being an anode attached to the radiator cap, and anodes that are built into block plugs. I have the NAPA coolant filter in all vehicles, so I wouldn't have to worry about any material flying off, but I was curious if anyone had actually used these before and noticed any actual results from them? I guess the only way one would know if they were working would be if the anodes showed wear. Any thoughts? TIA.