This sand does not seem to irritate the bottom of the ray and it is big enough that it does not stick like the smaller sand grains.
I have not had the scratching problems from the rays on acrylic or glass. However, I do have to be careful when scrubbing any algae that is close to the bottom of the tank. It can get stuck in the scrubber.
It has worked very well for me. The picture is a close up of the sand on my large 16"+ female motoro. You can see how large the grain is. When she moves, the sand rolls right off. I also added a picture of a pup on the sand.
Colin