Aren't those kind of stiff? I leave the mending to the wife. I'll ask her when she gets home from work although I see no reason why they won't work.

Edit: I just got done talking with my wife and she says that the reason for the backing is enforce the stitching at the tear. If you are working with a material where the stress on the tear will cause the stitching at the tear site to fail, you want to use a baking material that will withstand the stress at the tear. She said the iron on patch will work, but make sure that you sew it along with the tear to reinforce the tear site if you want the mend to last longer.