I only own the TZ-12 and can't comment on the other one. Though the given dimensions appear to be the same with a 3" blade and 7" OAL. Tolerances and fit and finish seem to be on the same level as a Sebenza if not higher. I also do like the satin finished titanium as opposed to the rough sandblast that Chris Reeve likes to have on his knives. I've carried it to work, though I didn't cut anything tougher than plastic ties(not the thick zip ties) and some thin cardboard. I'm talking USPS flat rate box kind of thin. Anything thicker and you'd have to exert more force to get through it, which can be difficult given the lack of jimping on the blade and the thin handles.
Haven't had a small Sebenza, but if it's anything like the Large cousin, it'll have respectably thick handles, especially with inlays. The one thing about the William Henry is that it's quite a bit thinner than most knives, so even if the dimensions are the same, the small Sebbie will give you a better grip due to thicker handles. Though I wouldn't choose Damascus for cutting cardboard to be honest. IIRC, Devin Thomas uses AEB-L for his damascus core, and AEB-L should be the same as 13C26, little to no carbides but will take and hold a razor edge easily. S30V or S35VN would be better for cardboard cutting, even though the heat treat doesn't push it as hard as I would like.
Again, if you're sure that the boxes you go through are of the thin variety and doesn't require you to punch a hole through a wall in order to get through it(because some thin pieces can be tough to cut through despite that), the William Henry should do fine. Anything tougher, and I'd go with the Sebenza. But again, I'd drop the damascus if you expect a lot of cardboard or abrasive material.