These are superb - I'm using Cherry MX Blues on one keyboard and Browns on another (I made a little effort to keep the noise down with the Browns).
Fitting the o-rings is a bit of a pain - on a full keyboard with numeric keypad, it took me around 90 mins, however, I was taking my time and I'm not at all mechanically minded. I ended up watching a YouTube video to figure out how to deal with the Spacebar, Return key etc. It's easy enough - I won't try to describe here.
I ordered red, They seem about right. Action is perfect, no real loss of travel, just much quieter whilst still very tactile.
I would agree with another reviewer that it feels less stressful when you are not bottoming out all the time. I'm not sure but I think there is a chance it may have improved my speed a little.
Well worth the money - I would say that I doubled up on the Spacebar and the Enter key - I was one ring short but had a spare in the other pack.
Both Blue and Browns are significantly quieter. I wished I had discovered these before ordering the Browns - I would have gone Blue with o-rings. You live and learn.
If you're considering it - order - I doubt you will regret it.