This thing looks like it’s pretty easy to use, and as a plus it can even handle a hard drive if you need to get rid of everything. A bit pricey though.
In my case I occasionally had to destroy a couple hundred, maybe once every 2 months. I just stood out at our dock with a ball peen hammer and set the CD’s one at a time on the rubber stops for trucks to back up against and whacked each one, case and all with the round end of the hammer. I opened a few and all of them were seriously damaged to the point I would have little worry of data recovery short of some kind of UberFBI crimelab grade reconstruction.
to simply render the media inoperable to ordinary mortals, I just score it several times on the label side with the point of a six inch nail - I find this does more damage per stroke than a knife.
For complete and secure destruction, grinding it to small chippings or incinerating it would seem best; rotary wire brushing the label side, unless done really thoroughly, might still leave some fragments of data intact (to absolutely determined and professional recovery experts).
Scratch the surface aggressively with a nail, as suggested, ensuring you get to the actual data layer underneath the outer layer of plastic.
Put scratched CD inside anything plastic, even something such as a section of bin liner. Have yourself a little outdoor CD barbeque where you heat the plastic-wrapped CD until it is significantly warped and/or melted (I used to put them on a grating over some lit firelighters inside a mini BBQ made from house bricks). Set aside to cool.
Nobody can get that data back.
Take off and nuke the CD from orbit; it’s the only way to be sure.