Had one in my wallet for years. Flew out of Columbus, Ohio, and the TSA guy picked it out of my wallet & took it away.
His reason was the tiny saw edge could cut through his blue non-latex glove. I said "really??" and for an answer he dumped out my carry-on and and looked at every square inch inside, then went through my clothes, shoes, toiletries, and accessories. He even jumbled up my neatly stowed charger cables. He then scooped up everything, shoved it mostly back in the bag, and waved me through with a smile.
I spent about 10 minutes refolding and carefully stowing all my stuff at the end of the counter. He kept glaring, but I calmly said nothing, did nothing, stayed blank.
(I'm really not comfortable in airports anymore.)
Anyway, it came in handy a few times, and I should pick up another one someday.