I think the idea is great. They are the right size for my shoes to just slip in. Only a couple of problems: First, they are pretty stiff and push down right where my toes join my feet -- ouch! Secondly, I have to shuffle when I walk, otherwise my shoe hits the back of the cover and causes me to misstep. With some improvement, they can be a great item!
I was skeptical when I purchased these shoe covers, particularly with my size 13 clodhoppers but they work just great. They are easy to slip on and off and are extremely light weight. I always have occasion to go in and out of the house throughout the day and it's a pain to have to taken my work shoes off every time. With the shoe in shoe I can leave my crummy garden shoes on without messing up the carpet and floors.