As they are right now, its just a test feature, far from production ready. The most simple clouds eat 50-60% of performance, in the complex clouds in the plugin examples it goes to 98-99%. Its just a nonsense. Its good to add new features, but this is absurd. Even more knowing that ACE Combat uses unreal and got decent volumetric clouds at 60 fps on consoles last year.
As it is right now, you will still have to make your own volumetric system.