#1, in the "Description" section, it says...
This kit comes with a 20-pin (2x10) 0.05" cable and a 10-pin (2x5) 0.05" cable.
#2, in the bullet points in the "Technical Details" section, it says...
- 20-pin, 0.1" target ribbon cable
10-pin, 0.1" target ribbon cable
I was only able to work out the correct size of the IDC cables by going up on the Segger website [2] and looking at the "Package Content" for the J-Link EDU Mini.
If anyone comes on this later, the correct cable to to use to connect to the Mini is a .05"/1.27mm pin pitch 10-pin ribbon cable, so if you want extras, this is the one to buy: https://www.adafruit.com/product/1675.
I hope this gets fixed in the product description for the J-Link EDU Mini at some point.
Thanks!
[1] https://www.adafruit.com/product/3571
[2] https://www.segger.com/products/debug-probes/j-link/models/j-link-edu-mini/