General hydro power grower

Do I start the seeds for the power grower in the rapid rooter thing? Do I need a dome on top?How big should they be before I put them in the power grower?

I prefer the wet towel method. tupperware container with paper towel folded in half. Wet towel, lay seeds out…a little separation so roots don’t tangle. cover place in warm dark place…check every 12 hrs. Once tap root is 1/4"+ long best not to let get over 1/2"…place in clear plastic cup with soil…with head at surface level …now you can watch the roots progress.
Once, the cup looks like a spider web…transplant to final location. If seedlings get too tall support with pipe cleaners loosely wrapped around the stem.