Mike: Several observations: I recently potted several cuttings of N.
kampotiana, two were in rockwool and three were in live sphagnum.
Although all survived, I felt the growth in the sphagnum was better.
Among other things, the rockwool did not stay firmly packed around the
stem of the cutting. Any movement of the bag tended to make the cutting
move around, potentially injuring the newly forming roots. The growth
of the rockwool cuttings was also a little slower, but not a great big
difference. I eventually removed all the rockwool I could and added
sphagnum. The other concern is getting rid of the rockwool, because its
so dense and matted, you can't really pull it off the plant because you
can't separate it to see the roots. So if you use it, it seems like you
are stuck with it.
Tom in Fl