Today I've received my keycaps, the Red/Black variant. Just installed on my das keyboard 4 professional (typing on them right now). I don't know if I've been lucky, but I expected way more problems... instead, everything went smoothly (almost). The only problem I've had, both the shift keys got stuck when pressed and did not come up. I smoothed them with a cutter on the inside and now there is no more friction, they work like a charm.
xankwondoIn my case, the top side of the shift keys. I pressed the keys slowly, on the center, left and right sides, trying to understand where the friction was. After a little smoothing, I put them back on the keyboard and repeated the process, until there was no more friction.