If Mothers Mag Wheel Polish or Flitz is more available to you, they work well on cardboard too. I probably wouldn't put them on leather because I think wax or soap based polish is better for the leather, but I am sure they would work.
Leather last longer and I like the feel of it better.
Cardboard is more readily available, works well, and I use it sometimes.
I think if anyone wants to try stropping and is reluctant to get into leather or not sure is they want to spend money on a strop, they should at least try cardboard. I have used magazine covers, envelopes, ribbed cardboard, etc, but I too like the back of a note book the best. The cardboard is abrasive by itself, but I like it loaded with a little more aggressive polishing compound the best for touch ups. I use cardboard bare when I need it too.
Gary