There are many growers that use rockwool from cloning right through the flowering. The only time you may have some problems is when you mix it with another media, such as clay pellets (Hydroton). In this case, rockwool holds water for a lot longer than hydroton.
That's what I'm doing right now, rockwool in the Hydroton. I started with a small 1" cube then transplanted it into a much bigger block of rockwool, in the hopes that the roots would take off more. My first little grow I started with 1" cubes of rockwool and trimmed it off the root system carefully then transplanted the root into just hydroton. I had some good success with that bought got too anxious and messed with the plant too much and broke the stem. What sort of problems will I run into with the large rockwool cube covered in hydroton. Aside from the wool holding water longer than the hydroton. Will I be just as successful with just using the hydroton?