I have one of the Italian Brown Mules and also one of the old German ones.
I kind of rate carbon steel on the steel in an old Mercator I have. Nothing to write home to mom about, but a decent carbon steel.
I found the old German Brown Mule steel to be at least as good as the Mercator, whereas the Italian model was much softer. After carrying for a time I realized that I still liked it better than, say, the 440A in a Rough Rider. I had to sharpen more often but it took a good edge. It was softer than a Mercator but not as soft as Opinel.
I've *heard* some of the Mules are made in China now, but that may or may not be internet gossip.
I also have an old German Coal Miner, Not carried it a bunch but would rate it with 440A(?), I dunno. The plastic handle stood up to back pocket carry for about a month with absolutely no issues and I think is more durable than it looks. Still, wouldn't buy another Coal Miner no matter what country of origin.
If I had the Italian Brown Mule purchase to do over I would save more and get a Case Sodbuster or a Queen Country Cousin for more $$$, as has been said. I really love the old German mule.
They both have quite a strong backspring, too strong. They can be "broken in" though.