I bought this despite the previous negative reviews since I needed something to help a ring stay in place, and these seemed like a good solution.
So far, I've only used one of these reducers on one ring, but it has stayed in place and has allowed me to wear a ring that is otherwise too large. Each time I wear the ring, it takes me a few minutes to get used to having a big, soft plastic lump on the underside of my finger, but, once I get used to the feel of it, it no longer bothers me. The reducer hasn't moved on my finger and has stayed in place.
Since the 6 reducers also come in various sizes, it's a good, quick, easy solution if you don't want to spend a lot on getting a ring re-sized.