In reading some of the other responses, I have agreed with some of them. One is marking pens, pencils or whatever. I have yet to find one that I really, really like. They all seem to have problems. I just took a hand quilting class, and the teacher uses, believe it or not, a No. 2 pencil to mark on the fabric. It comes out easily and leaves no marks. Who knew?
The second item I would put on my list is blade sharpeners. They do not work.
The third item on my list is scissor sharpeners. I have ruined several pairs of scissors using some of these devices that do not work. I bought one that got glowing reviews. I used it on a pair of scissors I have, and it now will not even cut paper. Why? In very, very small print it says do not use on left-handed scissors, and I bought this left-handed pair of scissors because I have a lot of trouble with scissors. Destroyed them. No more gadgets that sharpen scissors.
If you come across a pillow with batteries that massages your back, keep on walking. Does not have a long user life.
That's my list.