The OP actually answered his own question in the original post. It's technically a prohibited item, but whether a given TSA employee recognized it as such or just thinks it is a funky pen is just a matter of playing the odds.
Against a motivated attacker, particularly one with a firearm, I'd feel "armed" to the same extent whether I had a fine point Bic or the best tactical pen in the world. (Yes, I know, the most tactical of tactical pens are better at strikes.)
There's tactical water bottle caps, flashlights with strike bezels etc that might make it or prove useful. They all tend to provide the same illusion of security as the weaponized pens. (IE if you're good enough and cool headed enough to use one and prevail, you'd probably have prevailed with something else too and at best have purchased only a small amount of marginal utility.)
Mont Blanc's are allowed on planes last I knew, but clean the ink out of the fountain models before you take it on. Pressurization does bad things, makes a mess. I liked the Boheme personally for it's twist function. The platinum iridium nib will break skin nicely. Don't ask me how I learned that. Tends to bend it up and make is not so useful as a pen anymore though.
The metal Fisher (no relation) space pens meanwhile ARE generally allowed most everywhere, and you can strike and stab with them, and they won't leak ink. (As the name implies, you can use one in space. In days past the ads showed them being hammered through a baseball and still writing.)
As to weaponizing a slinky... They come in two sizes - large and small. I have destructive children - even been hit in the face with a large metal slinky? Hurts and is rather destructive. A creative person will find that to a degree the coils can be sharpened. They can also be used with a fishing weight, dropped into a sock or bag, as a nice black jack. The smaller slinky jr - a dollar at Target - works better for this. They can also be used as garrotes. (sp?).
Of course the ultimate weaponization is to realize that they are good spring steel, melt them and forge a rather neat little blade. Something fun to do with broken toys in the back yard.
Oh, you can use them as improvised radio antennas too. (Google it.) I used to have a shortwave set hooked up to a slinky antenna and it seemed to improve reception.
Zen and the art of the death slinky. Solemn nod.
Anyway....
