This is one of my must have items when i disappear into the woods and coast where i live, i think the fact its so small is brilliant, i always leave it in my day pack just to keep that great edge on your knife, just remember this will not make a butter knife into a scalpel, this is for maintenance of a sharp edge, i heard someone complain on another website about that.
All in all brilliant, a must have companion to your knives if you plan on being out for a few days with alot of bushcraft or carving usage, also keep a good quality leather belt with you just to put that surgical edge on :-)