They're perfect for any mechanical keyboard, they help (admittedly a little) to dampen the typing sound.

There isn't a big difference, but the product is good.

I have a keyboard with Gateron Brown switches, and putting a single O-ring on a keycap makes a radical change in sound. But if you put two, the sound is even better. I recommend it.

In the product description it says: "Colors come randomly (White/Yellow/Black) - you can add the color you want to the order notes, and if it's available, that color will be sent." I wrote in the order details that I wanted the white color. My order arrived today, and I received the yellow color. I think it would have been normal to receive an email informing me that that color was not available. The product itself is fine, but I would have preferred the transparent color, because on certain keys you can see the yellow ring, and I keep my keyboard on white.