I wasn't too thrilled with the Inka. The design seemed like a good idea, but it's kind of a pain to disassemble and reassemble into "full-length" mode and then disassemble and reassemble into "collapsed keychain" mode because you have to screw and unscrew part of it.

(When I say "it's a pain", I'm being relative, of course. Reassembling the pen only takes 10 seconds or so. But it's enough of an annoyance that I never felt like whipping it out to record my thoughts, thus defeating the whole point of carrying it around.)

You can use the pen without putting it back together into full-length mode, but that's about as enjoyable as writing with a golf-pencil... unless you have tiny hands, you probably won't want to write more than a few words that way.