HEST and RC-3 I carry on my belt using MALICE clips/straps. Both disappear completely under an untucked shirt (as well as the ESEE-4 carried the same way). Still figuring out the Izula, because dual MALICE clips don't work with it. Haven't tried just a single MALICE, though.... Hmmmmm.... Might have to try that... I really like the MALICE clips for carrying ESEE knives.
I started with a ball-chain (think dog-tags) on the Izula for neck carry, which worked quite well. But occasionally you could hear the sheath move over the chain links. But other than that, it worked quite well, and wasn't obvious... I don't think. Lately I've switched to coyote brown paracord, which I'm not sure I like. Seems to stick to the sheath more, which then moves the knot around and shift it from behind my neck. Which I don't like. I'm thinking of trying a shoulder carry, to place it along my side for a cross-draw carry.