IMPORTANT Outboard Motor Maintenance 

They do work,they are called sacrificial anodes and the general rule of thumb is to replace them once they are at 50%of original,on a trailered or lift kept boat they will last for years,I am a marine mechanic with over 45 years experience

I have heard that anodes are a scam? Like the car dealerships sell them here for rust in winters but there’s no proof they work.