Rockwool cube or slab is fine if you already know what you are doing, know the plant, know def symptoms, are familiar with nute solutions, etc. It's not something I would ever recommend to a beginner, or someone who plans to give plants an extended veg period.
The simple way to use rockwool is plug in rooted clones, flower immediately in SOG, run drip-to waste.
Personally, I prefer hydroton, because it's re-usable and getting rid of spent rockwool slab is gross and icky and can lead to security issues.