I have all the stalls done this way....slowly over several years, because of cost. I LOVE them and so do the horses. Our full size horse now lies down...something the old boy didn't do with just the regular rubber mats.
As for the Minis, I only put bedding in one corner for pee. Every day I sweep the floor of the stall and shovel up the wet bedding and the manure...only takes a few minutes compared to before. I find that without the old bedding, the barn is a LOT less dusty and it doesn't smell of amonia. A plus as I have some horses with heaves. Also, I think it is much warmer for them in the winter months as we have a concrete floor in the barn.
I had two separate companies install over the years and I have learned that the rubber chip underneath needs to be packed in tightly. The first guy spread the matresses out and we have bumps that make for wet spots and "urine travel paths". The second installer, packed a lot more into the stalls by compressing the matresses (made them cover a narrower area) and top dressed with loose chips as well. These stalls don't have places where the urine runs around the low spots....but the horses learned fairly quickly to use the bedding anyway(about 1/4 bale or shavings in the corner).
I have had horses on these stalls for quite a few years and am very happy with the durrability of the product. Besides, if the top did 'wear out' it is ONLY the top that needs replacing and the biggest cost is the rubber chip underneath that lasts 'forever'
As an added comment, my farrier loves trimming the foals in the stall with Mom as he gets to kneel on the cushy stuff <G> It sure is softer for the horse's legs too!