You want one 3" OAL - are you going to carry it in a locket or something? Three inches is about the length of your index finger - visualize that as a knife. How many fingers can you get on it and still have any finger left to simulate a blade? That's a weird way to say it, I guess but grab your index finger so that you leave one inch of it (fingertip to first knuckle) sticking out. It would be tough to do much in comfort with a knife of that size, IMO.
I've got a Becker BK13 that gets little to no use because it's just too tiny at approx 5" OAL. I could use it but the handle is only long enough for me to get about 2.5 fingers on it and Candiru looks to be about the same. There's a reason ESEE Izula, Becker BK11 and BK14 are so popular in the neck knife niche.
I'd go with one of those three - personally, I like the BK11.
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Beckerhead #42