Get the Booster straps and decide for yourself. Try them both ways. It’s not like they’re expensive. If you don’t like them you can swap back the original power straps that came with your boots.
Myself, I have them under the shell, very snug, and barely have to buckle my boots. Done thusly, I find they keep my boots responsive, regardless of how much or how little I buckle.
There we go. In my case as I ski, I keep ratcheting down the top buckles more and more, including the OE power strap (non-elastic) seeking more pressure on the tongues. This is as they've packed in - still relatively 'new' < 30 ski days on them. But I'm getting near bottoming out the buckles without moving them and the booster strap seems like it was designed to solve this issue for me.