That's likely the tool I'm using. Maybe mine's from a bad batch, not enough carbon in the alloy or improperly heat-treated. Use it on a few 32" loops and it's easy to see how the flat has dug into it. (The flat file in that kit is a keeper.) You seldom have to do that on a given chain of course, but still I'd expect a bit more durability. Really easy to see the metallurgical difference from the "File-O-Plate".
I like how the chain cuts after filing the depth gauges with that guide, on a 576XP w/32" milling. What's your take on how it preps the chain?