Haven't been to Ben Nevis, but from photos and video the CMD arete looks pretty similar to the "knife edge" on Katahdin in terms of difficulty. The CMD arete is probably a little narrower than the Katahdin Knife Edge (KKE), and the KKE is probably more solid rock, which means you can (for most of its length) stand away from the very top without worrying about riding a landslide all the way down. (Most of it is more like the second video below than like the first.) The KKE does have about 700m vertical exposure on one side, and one notch where you have to climb maybe ten feet of almost vertical, down then back up.
In short, if your'e scared of heights, you probably won't like the KKE either. http://www.youtube.com/watch?v=BKRZiy_sLcg http://www.youtube.com/watch?feature=en ... BfTVHuqeMY