Interesting,but?
I want to place my hot tub next to my patio. What benefit is there to using "The Spa Level-R™" on a non concrete surface?
After the ground is leveled, "The Spa Level-R™" can be placed down as a support platform. This will keep your hot tub raised off the ground and away from moisture.
If I am going to the effort of leveling the ground before I put it down, why would I need it?
Still not a bad idea.