So far I have only had them on for a few days but haven't had any issues whatsoever with grip, even this morning when it was wet.
As for the aftermarket -> to the best of my knowledge these pedals actually came stock on the STi so there should be no issues there either.

Edit: just re-read your comment Jezza and realised I had the same problem with the clutch lining come off...hence how I stumbled across the STi ones lol