John, I saw this far to late to comment, but I have used the s&w pen for a couple of years now. I have never used it with true serious intent, but I have done two serious restraints with it at work to prove a concept to some non-believers. I have nothing but love for it, plus the price was decent. I leave it at work, but it is in my shirt pocket every second of my workday.
Honestly, if I really needed to defend myself at work, the pen would be my first choice over the knife. There are a lot of reasons for that, but the biggest one is I really don't want to have to cut someone up, along with legal problems related to carrying a knife at work. I get away with it, but strictly speaking I am not supposed to carry anything larger than a little penknife. Also, and perhaps naively, I think my wrestling background, though many years in the past, lends itself more readily to pen as opposed to knife "combatives". 16years of being a mat rat gives me a high comfort level with applying pain compliance techniques, you see.