I've got a 2 blade #47 in orange delrin and one in Nifebrite Acrylic. The Nifebrite one is approximately the thickness of a delrin/micarta single blade 47 or 71, albeit much heavier. It's a chunk of a knife either way. The pen is long enough to count as a full-sized blade - it's only a hair shorter than the blade(s) on a Case mini trapper (3.5" closed). I don't really carry either them, because as I said it's a hefty chunk of a knife. I do however very often carry my single blade Nifebrite #47, and for a good time carried an orange delrin one before passing it on to someone else. I always have my Cybertool 29 in my other pocket, so the pen blade on the #47 is redundant for me. The pen also has a very stiff pull. If a Victorinox Soldier/Pioneer is a 5, I'd say the pen on the #47 is an 8. Not impossible to open, but don't be surprised if you find yourself filing or trimming your thumbnail's broken off chips once in a while. I'd say the sheepsfoot blade is a solid 6-6.5 on the pull, but there's enough exposed (even on the 2 blade) that you can pinch it open rather than using your thumbnail.
I very much like the way GEC does their sheepsfoots (sheepsfeet?), at least on the #47. It's far from a wharncliffe, but it's got more of a tip than most other companies make their sheepsfoot blades. It's also ground very thinly to the edge, and combined with the O-1 tool steel, you basically have a utility knife that isn't one of those heavy Stanley ones or those flimsy retractable ones with the break-off pieces that scare the heck out of me because the dang pieces are designed to break off.