I love these notebooks and have purchased well over a dozen (over time!). I use either the French ruled or the regular lined variety. I have been auditing classes at UW Madison and use Clairefontaine notebooks for note taking.
I have found that the nibs of my fountain pens write with a finer line on this paper so I prefer to use a medium nib pen. The paper is heavy and smooth. No show-through using Edelstein black ink.
I have only used the wire bound notebooks. I recommend them!