I have them in my barn and LOVE them!!! Affordable, easy to install, and only 50lbs per stall!! They do not move around or shift once installed, use less shavings since they are water/liquid permeable and even with stall walkers they stay put.
When we installed ours we had hard packed dirt and just put them over top, did not use the gravel base and have had no issues!
Much easier and nicer than rubber matts