We bought cheapies at Black Dome Outfitters before Stecoah to NOC for just in case....they were not used but I was so impressed with the theory I upgraded before our last hike to the CMI version (via REI).
From Wyah Gap to NOC after Wyah Bald we both strapped the instep crampons to out boots for a 1-2mile test run. After feeling them grip not only ice but solid stone I can say I was impressed and cant see any winter hike without them...beyond that, they also work for muddy terrain and I have to wonder about the increased safety one really has with hiking poles and these crampons installed.
Just remember to remove them before setting up your tent, the CMI version has very very sharp points that will piece most any gear you own.

I use the climb-high 6-point instep cramp-ons when hiking in snow/ice up to a foot deep. When it gets deeper than that I break out my snowshoes. Mine are kind of a pain when they clog with snow, and I have just this morning ordered a pair of the 4 point ones. I feel they will serve the same purpose, and that having a solid central plate will prevent clogging. Less straps too. It can be a pain in the ass putting the 6 points on in cold-weather. Never tried them on just rock or mud though. I usually have enough traction with just my boots (soon to be burly trail-runners). Did you get the Neoprene or Poly-Straps?

***EDIT***

I hike on a network of trails intersecting throughout the central mass state-forests during the winter. A particular hike I do about 5 times a month consists of 3 miles up a trail packed down by snowmobiles, and then 1-2 miles of rugged snowshoeing down a rocky trail which sees little use. The snowmobile packed snow is dense and often icy, so I wear my crampons up to the top of the mountain, and then swap to my snowshoes on my rugged descent. Sometimes the snow is too deep or the trails are too clogged with fallen trees, which prevents the snowmobilers from breaking virgin paths. In these cases, it's snowshoes all the way baby (and a very tiring 4-5 miles).

Im thinking of making a pair of instep ice cleats like sweeper made from a of steel,wood mending plates they cost about 2 bucks to make and weigh about 2.5 ozs

http://www.unc.edu/~mkirk/myog.html

Streamweaver

I own instep crampons, but they don't get much use. Occassionally get carried for "just in case" in late fall. However, in winter, I'm usually carrying either full crampons or snowshoes or both. The crampons on my MSR snowshoes are so good that I usually keep them on all kinds of mixed and crusty conditions where insteps might otherwise be used. I do use insteps with my sneakers for taking the dog outside when my yard is really crusty.