I was looking for a sharpener for my EGO electric chainsaw, which has a 3/8" chain pitch but clearly states to use a 4.5mm file diameter (11/64") for sharpening the teeth.
This particular sharpener design (which appears to originate from Stihl) is ingenious and is getting rave reviews. Unfortunately, the only file size these sharpeners come with for a low-profile chain is the 4.0mm file diameter (5/32").
I bought the less expensive Mempa tool and a 2-pack 4.5mm diameter file set by Makita (D-75708) intending to replace the round tooth files. Upon receipt of both, it looked like I could replace the round files with the larger 4.5mm file set as EGO requires, but I would likely have to drill out some of the plastic in the holder ends. However, when I put my 3.5X magnifying headset on, I saw that the 4.0mm files (5/32") that came with this sharpener were a perfect match to the tooth curvature of my factory chain, while the larger 4.5mm files I purchased separately were actually oversized when viewed under magnification. Glad I discovered this before drilling out the holes in the holder!
I put the Mempa tool back together as received, and it worked great!
I can't explain why the 5/32" files were a much better fit for my EGO chain teeth (versus EGO's recommendation for 4.5mm file diameter (11/64")), but this tool as received worked just great for me!
The tool comes with markings on the end, which I filled in with a black Sharpie to help reinforce saw position and filing direction. I also recommend marking each tooth sharpened with a Sharpie as you go along (to be sure you actually sharpen each tooth with only one sequence) and cleaning off any debris on the files with a soft brass bristle brush in between teeth. I used my magnification headset during sharpening to ensure the tooth fit and 30-degree sharpening angle were maintained.
I used three strokes per tooth based on a video I had seen, and it worked great as a maintenance sharpening (if you have substantial tooth damage, it will obviously require more). The same video suggested putting the center of the flat bar carefully in a vice with medium pressure to stabilize the saw while sharpening, which also worked well for me.