I'm nowhere near an expert on this, but let me explain my logic in the choice of closed loop versus power heads. Once you install (drill) for closed loop, the location of the outflow pipes are fixed. As you do your rockwork or as things grow out, that’s it, the outflows stay where they were drilled. With power heads, you can move them where you need the flow. If it changes as things grow or you redo rockwork, you move the power heads. That’s my cheap two cents.