Smith's Diamond Combination Sharpener

Keeping our sharp tools sharp is very important to keeping them performing at a high level.  At home this is an easy task.  You have oils, stones, etc.  Everything is right there.  Now taking all that with you in the field is another story.  Especially when weight and size is an issue.  I have tried a few small sharpeners in my time.  And I have finally found one I really like.  The Smith's Diamond Combination Sharpener.
I have used this one for over a year now and it has been one of the best additions to my gear bag.  Here are some specs from Smith's website:

Collapsed Size:     4" x 1"
Dual sided, Coarse(325 grit)/Fine(750 grit)
Fish hook sharpening groove
Finger guard
Cost:   around $15-20

First thing to clear up is the size.  The handle is 4 inches, but the total collapsed length is 6.25 inches.  The length of the sharpening surface is just under 4 inches, about 3 7/8".  Still a compact size though that is easy to carry in your pack.

 
One of my favorite things about this sharpener is you can use it dry, with water, or oil lubricant.  I have tried all three and they are all effective.  Most of the time in the field you don't need a full blown sharpening session.  Quick touch-ups here and there are all you need and this is perfect for that.  Now with that said you could do some heavy sharpening with it if you needed it to.

 
The main pros of this sharpener is how compact it is, and that it's dual sided.  The diamond stone works well for high carbon steels and stainless steels making it great for your knives and axes.  It has put a very sharp edge on all my knives and axes.  The handle is rubber and provides a secure grip.  This does not slide around when using it.  Even if your hands are wet or sweaty.   The stone attachment stays secured to the handle.  I haven't had any issues with the stone part coming loose when attached to the handle.  I don't really have any cons I can think of.  If it were bigger it wouldn't be as handy for field carry, so that would defeat the purpose of it being an ideal field sharpener.  Overall I would highly recommend this sharpener for field carry.