Hmm. I seriously doubt it's a leather tool. For edging (knocking the sharp 90° corner off of a belt blank, rein or other strap of leather) a simple "edger" does the job. Chilli described one partially, i.e. "semi-round". My "edger" for dressing the corners of a new strap is a round shank w/ a half-round cutout like a carving gouge that does the deed. Beyond that, I dunno what that tool is for but I'm with Amecks about sending them some photos and query.
Oh, and color me olde-fashioned but I've never trusted simply compressing the edge of a new strap into the shape I want. Most of my leatherwork was/is for horse harness, reins, belt-blanks or the like, all of which are prone to being used in moisture that'd cause the leather to re-swell back to it's original 90° shape. S'pose I gotta add that I don't "treat" leather, beyond neatsfoot oil and only rarely coloring/dying it.
I cut all my edges, straight or round (chamferred or rounded), they never move or change after compressing and finishing. You don't compress an edge to form it always (you could, but it would be a lot of work) it just cleans a cut edge up. The edge finish is just a little thicker/ harder. Kind of like a shellac. It is used for the belts that go around your waist. For utilitarian work, tool straps / pouches/ etc. your method can be used. But if you are making a belt that will sell for a few hundred dollars, you better finish it right. Its the difference between a bull rider and a cutting horse. One gets beat up and put away wet. The other one spends 40 or 50 thou on a horse and another 50 or 60 thou on a truck every year.
Finished correctly, veg tanned leather will never swell back after working, chrome tanned cannot be worked. Period. It will always go back to its finish. Most would use finished, like a latigo, for reins and outdoor gear / straps. You cannot tool it. Bottom line is, I agree with you, Bear. But we were talking apples vs oranges. Or rather vegetable vs chemical.
BTW - I didn't say it was a leather tool, just that if it was it looked more like an edger or liner if it was. It was in response to someone dismissing someone elses comment just because it didn't look like it was a cutter.
One last thing, old fashioned? Heck there's hardly nothing new in leatherwork. Even the biggest retailers still sell books and patterns from the 50's / 60's. Al Stollman has more titles at The Leather Factory than most all the rest. The fact that you have an edger and knew how you use it already had you pegged, along with me, as old fashioned. That's why old leather tools are so hot always. They are still the best working tools. Everything modern is too light weight or finished to ugly
Chilly