I love these things. I bought the blues for my Ducky Zero with blue switches. It cut the noise down by about half (at least) which was one of the main reasons I bought them. In my opinion it also significantly improved the feel. Lots of people have complained of a somewhat mushy feeling but, I must disagree with those comments. I personally love the feel now. The travel distance is certainly much less but you don't lost the "click" or the tactile feedback of typing with MX switches, and particularly blues. It has made typing large documents (the one thing about blues that I personally didn't really like) much more enjoyable for me. It has also improved my typing speed. Now, one thing I will recommend is that you give them a little bit of time to break in so to speak. When you first put them on some of the keys will require a significantly harder key press but this goes away rather quickly. In no time the o-rings will break in and you won't need to worry about typing with a harder press at all. At most it'll should take about a week but, that'll obviously all depend on how much typing you do.
All in all, I recommend these o-rings and I think that they are a particularly great addition to any keyboard using MX-blue switches. Enjoy folks!