Just a though: if Blademaster's variant on the Pro-Filer (which they don't seem to call Pro-Filer) has no extensions, just a gap, does that make it harder to align, because the gap isn't as high as the gap+extension? But does it also mean that the tool could sharpen some current generation Matrix and Paramount blades that Pro-Filer might have trouble with?
Even if the material of the chassis is soft enough that the chassis itself does not scratch polished chrome (or stainless) surfaces, scratches will be inevitable (in the absence of tape or other protective coating on the polished surfaces). As you perform the hand grinding, particles of abrasive or steel will come loose and fall in between the chassis and polished surfaces and cause scratches.
Not if the tool is UNDER the blade. E.g., if you hold the tool with a vice, as I think Bill_S once suggested, or maybe in your hand, though holding it underneath with my hand makes it a little harder to center it.
As I've said before, I have no trained tool skills, but have to learn from my mistakes. So I have indeed made some scratches. I had to learn to lubricate the sides of the blade, by wetting them - which helps.
The problem is, I like to see what I am doing (so I only bump into the toe pick), so I do tend to hold the tool ABOVE the blade. So I have have some minor scratches.
Just call the scratches an "extended chrome relief" feature.
Great idea! Claim the scratches help orient and redirect the blade, or something else vaguely plausible.
The sanding drum that Kaitsu made looks a bit challenging to make - you might need a pretty high accuracy 3D printer. There are commercially available sanding drums, and sanding sleeves that fit them. I wonder if any of them could do the job.