I bought some cheap gutter guards from ACO hardware....the manager recommended them....they took forever to snap onto my gutters & they leak all around the entire house. They DO keep the buds, helicopters & leaves out so I do not have to go up on the roof to clean them out anymore, but you cannot get into the house without getting drenched, if it rains hard & I MEAN DRENCHED...like you just took a bath in your clothes..so you have to have an umbrella to get in the house.
Dust Off -- one drop of that stuff will RUIN your computer or any sensitive electronics. I've never seen a product less suited to the use for which it is marketed.
I haven't purchased any terrible inventions, but I've seen some. Portable toilet paper holder. It looks like a plunger hat XD
Just the opposite: Nads hair remover works quite well!