I found the pen blade very useful, on a Case Peanut a while back, for cutting some small-diameter holes in some roof insulation. My Dad & I were on the roof investigating some damage done by burrowing bugs, which had been boring into the closed-cell foam insulation. I was using the blade to probe for voids created by the bugs, and doing a little excavating of material in the process. The narrowness of the pen blade and the piercing tip were perfectly suited to such work. The working principle is very similar to that behind the narrow 'melon tester' blades on other knives, to be used for cutting circular plugs out of fruit samples.
David