I don't care for Derbys but I love the Personna Reds. The Derby's don't cut as well and are more prone to irritating my skin. I can see the difference in the blade edges when examined up close.
Personna Red 200x New
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Derby Extra 200x New
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I completely forgot that I have one of these 250X microscopes. I think I'll photograph the edges of the various blades I use and post them to the forum.
The photo of the Derby Extra looks just like my blade felt this morning. That's a really poor job at manufacturing.