You are so right! One of my favorite examples of this is the compost tumbler! My neighbor was moving and offering his double compost tumbler for 50$ so I bought it, thinking that it would speed up my compost pile. How wrong I was! It was actually much harder to use than my regular compost pile because one had to put all of the browns and greens in the tumbler at the same time. I couldn't add freshly pulled weeds or raked leaves each day, because it would spoil the mix. IN addition, I found it difficult to turn the handle. I never any compost out of this thing. I sold it, however, for 100$. So at least I made a nice profit!!
My very favorite garden tool is the root knife I got from an American company called Lee Valley Tools. It is sturdy, sharp, the right size for my hand, and I can use it for almost everything from cutting thick roots to dividing perennials. It's a great tool!
My favorite greenhouse tool is a chopstick! I can lift tender leaves, move dirt around in pots, etc using a simple chopstick.