This is an image of a step I put into the tail of my original 10'4 a couple of years ago. Not as deep as the Konas', the step has been in windsurfing for years now, it was originally for the new breed of wide, short race boards of the 90's.
What it did to my old board was give it another life and loosened the board up dramatically. This has lead to my current late tail lift designs, but without the step.
Yes the step has merit not so much for surfing, definitely for windsurfing. I was showing Bill Hamilton (Lairds dad, he visits Coffs regularly for hols) early last year on a tiny surf day and he was telling me that some of the crew in Hawaii doing SUP boards actually have incorporated the step as part of their shorter board designs.
So yes they do work for surfing.
Got up early and had to wait for daylight, no waves tho.
Rod