I wonder if it has to do with the stiffness of the rings? FWIW, when I bought my first Quarq you couldn't use Praxis at all due to calibration issues. That is how I ended up with the Stronglight rings.
Don't get me wrong, the shifting has been nothing short of superb. I've just been itching to give Praxis a try from their debut.
i have bent 2 Stronglight CT2 53 tooth chainrings in 3 years on my Quarq. very odd. shifting is ok, but not as nice as Campagnolo chainrings. I have the Praxis rings on my new Riken, and thus far they have been underwhelming. the change from the 39 to the 53 is a bit slow, and sometimes it refuses to budge. i had 3 different mechanics diagnose it to no avail. i called Praxis and they were as perplexed as i was and to their credit, they sent me a new set. initially, i still had the problem (thought it was somewhat alleviated), and it seems to have gone away somewhat but i haven't ridden the bike this winter as i have a CAAD10 (with a Cinqo and bent Stronglight CT2's) for winter duty. it's not as perfect as i was hoping it was going to be.
nothing beats the original Campagnolo rings for smooth shifting.