I am a humongous Surefire fan, they are one of the few things I recommend by brand, but I gotta admit to being a little put off by the Defender. The beauty part of a Surefire like the 6P or my personal favorite and EDC the E2E is that it isnt a weapon, though it certainly is an effective yarawa or kubaton. My concern is that I wouldnt be able to get the Defender into a secure area like a federal building or anyplace with a "no-weapons" policy, while my E2E goes everywhere, including aircraft.
I also have some questions about it's efficacy as a weapon - it looks guaranteed to break the skin, leading to all kinds of body-fluid-goo issues, but is probably nowhere as effective at breaking the skin as a knife. In other words, it probably does a really irritating amount of damage when you dont necessarily want it to, and not enough when you do.
Now I find that I am talking myself into getting one just to see how wrong I may be.