I have had the double SUP board lock rack for 3 years now. Great product and way quieter than straps (1 board or 2 boards and any combination of types of boards), plus very secure at high wind speed.
For me ideal and pretty much 5 days a week I will have a board on the roof (wishful thinking mainly), and I am comfortable with leaving the boards in public places as a result.
@micksmith - Probably correct in the image's you have referred to, but in reality, if they are on tight, it is actually difficult to remove as the rubber matting sticks well so I have not had this problem.
To me a big bonus is easy, one man loading in high wind conditions will save one money in repairs, and I worry less about damaging my boards trying to tighten the straps to much.