I use rockwool cubes for creating rooting my clones, fire away any questions you have
You will see in the link below my last batch of clones.
I have found when teaching people to clone it is very often the grip they have on the stem when inserting the cutting into the medium causes most failures as I have watched and instructed at every other step.
Its a fine line between firm and over firm where the stem crushes, this is less of a problem in air cloners as you dont have to insert the stem into the rockwool cube (spiking it in), instead usually into a foam insert with a slice in to place instead of spiking it in.
I usually have roots from cuttings taken from 4-7 days strain dependant