For me, the mk2 was just a hair sibilant. Well within what I am able to tolerate. It's slightly bright, but enjoyably so. I was able to get better insertion depth with the mk2 than the mk1.
With the mk1, I couldn't quite get a good seal for the treble to behave, or at least the bass drop off was so significant that it couldn't balance the treble. LFF and Anax had no seal issues with the mk1, so the prefer it because of the better bass quality.