Nothing inherently wrong with rockwool if you treat it like rockwool.
A big trick to plugs of any sort is that once the roots have gone beyond the plug, stop letting the plug get wet at any time. So if you are flood/drain, you would check that your max flood level comes up to JUST BELOW the level of the bottom of the starter plug/cube, and does not soak it every time, which can lead to a girdling stem rot. And that is tragic.