I fitted the pedal kit myself a couple of years ago. I can absolutely assure
mindbrother that there is no way they can affect the movement or performance of the pedals themselves.
There was a lot of conversation on another forum

(mostly from a numpty) who thought they might be slippery. Again, after 40K miles in all weathers they weren't slippy; in fact probably less than the standard rubbers.
It's a simple DIY job to fit them (if you have a cordless drill for a single hole in the metal acellerator pedal) and I smiled every time I got in the car in the dark, when the footwell light shows them off. Hardly anyone knew they were there, but that's part of the secret satisfaction of an XF
PS I'm a newbie on this forum (some may know me from the other one). I guess I'll have to earn my stripes all over again!