Jason, you beat me to it with your posting as I wanted to write a recommendation for the Gransfors puck.
I own one since one year, after some hesitation about the price.
It is used for sharpening the axes and works very well. The rubber casing makes it transportable and also protects the fingertips when sliding the stone over/against the edge in circular motions
The fine side is quite fine, about 1000 (compared with a japanese waterstone), the coarse is still not that coarse at about 600. Both figures are just a guess, someone else might know better.
So its possible to get -in the field- a paper-slicing edge on an axe with this stone, but removing bigger nicks would be very time consuming.
I also started using the puck for sharpening my knives. Out of pure boredom yesterday I used it to sharpen a 10cm, 12C27 blade from Brusletto and it works ok. I could do only small circular movements along the edge, so a bit more concentration was needed to work the whole lenght of the edge equally and it took longer.
But it did sharpen the blade and so this GB puck will become the constant companion in my pack and be used to re-sharpen everything in the fiel:d, axe, puukko, Leuku.
Highly recommended!!!