the 12 inch is very good for a lot of things, like, everyday, around the house, garden, and is/would-be a joy to carry for all things. Until you needed to do anything longer than say 30-45 minutes, then you might wish you had a bit more oomph in your tool - that's the point i'd go get something bettah... the 15 inch *esp* for camping/outdoors would be ideal instead. still a joy, but you wouldn't be thinking "mmm, wish i had something bigger" until you're doing a bit more than a couple hours of making kindling, stakes, trimming branches and things. i wouldn't consider taking trees down with it, much - okay, maybe one, and it'll do it, just don't expect say, 18 inches of goodness out of it...
comparison wise, the pens are very nearly like GRSes, with a bit more belly and potential on the chopping, different look, and a subtle different feel. they are QUITE good feeling if you're into bolos, machaxs, or even bowies. just right.
for true goodness, ditch the scabbard and karda/chakma, and get a thin sheath rig (leather/kydex). then you'll LOVE it. talk to Dan Koster (the man), who by the way had a *SLIGHT* hand in the Pen design ;> Pendentively speaking
bladite