Yea, actually thinking more about it now, I'd probably avoid the paper cutter.
I've had enough bad cuts from using paper cutters, and you can't really risk destroying more than a couple of these unless you want to spend a lot.
I was actually thinking maybe Hypersphere does want to adjust the cut of all the rings, because you could actually use less material/get higher yields if all the rings had this little cut at the top. They still work with stock Topre just fine, the missing piece is just a symmetry thing (which might bug people, I dunno, doesn't affect the noise).
If you had the two flat sides right against each-other on the stencil, you'd actually save 2-4mm of material for each row (I assume they line these up in a grid and cut them). So, less material used, and it fits all the Topre sliders (RGB + Original)
(Except that pesky 87u Left Ctrl).
Or if you added 4 flat sides to all of the rings and made them more square, it would also lead to higher yields because you could put all the rings next to each other on the stencil.