One important reason why the Forges de Niaux 200s stay sharp longer than Ingersolls: The Niauxs start out with ~3/4″ of bevel, vs ~5/8″ on the Ingersolls (see photo).
That’s over 1.5° smaller angle (13 vs 14.5°) at the edge, which is a significant difference for cutting ability and ease of penetration of the soil. Not to mention that it gives you a bit more bevel at the outset (after half the bevel is gone, the cutting ability is truly lousy—so starting out with 1/8″ more bevel just gives you that longer wear life while maintaining decent cutting ability, as blade diameter gets whittled away). (Larger diameter blades aren’t the answer to longevity; read why here.)
This is in addition to the greater hardness at the edge of the Niaux 200s. Greater lifespan and better cutting ability make these the new benchmark for blade performance on single-disc drills. Exapta has a good supply of Niaux 200s for early 2019. (After we exhaust our supply that was purchased at 2018 pricing from the factory, the price will increase several dollars apiece, so stock up!)