I am happy to say I am writing from a CM Quickfire XT, equipped with a Vortex Thick PBT 104 keyset (Orange on White Doubleshot).
It arrived yesterday and I was eager to install them. Finally I have this sweet, sweet PBT feel
Here is my story :
The board with original keycaps removed :
Surprisingly, I managed to remove all the caps with my bear fingers and without the help of a keycap remover - my other CM Quickfire XT is a Cherry MX Blue one, and its caps can not be removed with bear fingers!
The board was a bit dirty :
I cleared it a bit :
New caps :
Job done :
I had O-rings ready for install, but when I tried both with and without them, I chose not to install them. The sound is way better without O-rings!
So my verdict is Vortex caps are good (at least this model).