I actually carry that bungy all the time, b/c I often carry on a booster seat, too, and it comes in handy. I've only been warned about the bungy once, when I wasn't using it and had it stowed around the handle of my carryon.
It was just the silliness of thinking it was a possible weapon that got to me. I could see that they might have concerns about one with heavy metal hooks, as one might conceivably use them like a club, I suppose. However, this one (from Lewis N. Clark) has lightweight plastic hooks, so that possibility is not an issue.
I really don't think that restricting little everyday tools (other than box cutters and large knives) is all that important in the security battle; I think that what counts most is keeping the cockpit secure and keeping people who lie about their legal status or identity off of flights altogether. Pilots used to all carry Leatherman tools, but those became forbidden under the new rules. Personally, I *want* the pilot to have a pliers and a penknife handy if a switch breaks or a crucial wire gets disconnected during flight.