I can only speak to the Renzetti, and there it depends of which model Traveler. Older ones have knobbed screw to tighten on a hook, and a smaller find adjustment screw, which would both be on the wrong side of the vise for a left handed tyer. The newer (like made in this century) use a lever under the head to tighten the hook, so you don't need to reach around the vise every time. The fine adjustment screw will still be on the back, though.
Some models of Renzetti (and I can't remember if any of the Travelers are among these) have a ratchet mechanism to turn the vise in rotary mode. These turn the wrong way if you wrap counter-clockwise looking from the eye end of the hook. (Not all lefties do.)
