I bought these because I'm moving to a shared house and while I like my Filco Majestouch keyboard, the keys were bottoming out and make quite a lot of noise. I bought these because I'd heard they were good for quietening down the keys.
They definitely help, though if I was ordering again I'd go for the slightly thinner red ones, because these do affect the key travel just a little bit, meaning that I've had to get used to what feels like a slightly different keyboard. The good news is that it's a lot quieter, and once I was used to it, I could type as fast and as precisely as before.
The only thing I would add is that they are very fiddly and slightly difficult to fit over the underside of the keys, if you have large fingers like I do. Some kind of applicator tool would have been helpful, though this is a minor concern. After fitting they did also give me a bit of a worry because it took a while before they were 'settled' on the keys, meaning that each key had to be pressed quite a few times before it could be touch-typed with.
All that said these worked fine for an after-market solution, and they achieved the goal of making an excellent keyboard quieter without compromising (for long) on its ease of use....