All lawnmower blades tend to be within the same rockwell hardness range. So there is variation but all within the same category. Some will add a coating to the cutting edge to extend sharpness periods.
OH , now i recall how we tested hardness long time ago .
If it can be easily filed with a good mill bastard it's not very hard . If it files more like a Cold Chisel it's a tougher better blade . IMO