I could never get those to work for me.

I've so far only used the 6 and 7 mm ones, and getting the discs out is not that easy. Each of the holes is bored all the way through the lower (and upper) parts to its actual diameter, they don't open up like modelling ones do. This meant that the discs "stick" toward the bottom, and to get them out required pushing with a tool that fits through, but not with the punch itself.

The edges are fairly sharp. It looks like the punches are simply sawn from a length of steel rod — you can see parallel lines on them at both ends — without any more work done on them.

I searched on Amazon for disc cutter tool (after discovering that this is what they seem to be advertised as) and found two or three basic types being offered for varying prices by what seems to be different vendors, so I bought the cheapest one among them. The exact one I ordered is this but you may notice that the punches there are more elaborate than the ones I actually received. Also, I notice the price has gone up by about €10 in the week and a half since I ordered it …