Overview & First Impressions
Most knife launches play it safe with one familiar steel. Trivisa put ZDP-189 in the Scarab Ultra and pushed it to 65 to 67 HRC, which is the sort of number that makes sharpeners sweat and steel nerds grin. Same 2.99 inch blade, same 2.36 ounce titanium frame, same crossbar lock as the M390 version. The difference is entirely in how long the edge lasts and how much respect you owe the sharpening bench.
Materials & Construction
ZDP-189 is a Hitachi powder steel with roughly three percent carbon and twenty percent chromium, sandwiched here between softer cladding so the thin core does not crack. At this hardness it holds a 15 degree edge through things that would roll a 58 HRC blade flat. The trade is brittleness: no prying, no chopping, no lateral heroics. The glass bead blast finish leaves a matte grey surface that scratches less visibly than satin.
Design & Details
Nothing about the geometry shouts. A narrow drop point, a subtle swedge, a comfortable finger choil and jimping exactly where your thumb sits. It is the kind of shape that disappears into work, which is what you want from folding knives built around a hard, thin edge. The closed length of 3.8 inches and sub-2.4 ounce weight mean it vanishes in dress trousers, and the crossbar lock keeps one handed closing honest with cold fingers.
Real-World Use
Cutting rope, trimming leather, opening feed sacks and slicing fruit are where a 67 HRC edge feels like cheating. I ran it through a week of warehouse cardboard and it still shaved, which is not something I can say about the softer steel sitting in my other pocket. It is a poor choice for scraping paint or cutting on a ceramic plate, and a terrible choice for anything involving a twisting motion. Treat it like a scalpel and it will outlast your patience.
Ownership Notes
Sharpening is the real cost of ownership. A 67 HRC edge does not respond to a $20 combo stone and a casual wrist; you need diamond plates, a guided system helps enormously, and you should stop the moment the edge bites. Micro chipping from lateral load is repairable but tedious. Keep it dry, oil the pivot lightly, and resist the urge to dress up the lanyard with heavy metal beads that could knock against the blade spine. If you already own a couple of EDC knives in softer steel, this is the upgrade that finally makes edge retention feel like a solved problem rather than a marketing claim.
Who Is This For?
Buy this if you cut a lot of abrasive material and hate touching up an edge. It rewards the person who owns a guided sharpener and enjoys the ritual. Avoid it if this is your first good knife, if you work outdoors in freezing wet conditions where a chipped edge ruins a trip, or if you want one blade to do everything including light prying. The M390 Scarab is the friendlier sibling for that job.
Final Verdict
The Ultra-S is the most interesting knife in the Scarab family precisely because it is not the easy choice. ZDP-189 at this hardness in a 2.36 ounce titanium crossbar folder is a specialist tool, and it is priced like a specialist tool rather than a novelty. EdcMall stocks it alongside the M390 variants, so you can compare both in the same cart and pick the one that matches how you actually cut.
