we changed to this size when our cat turned 1. No issue with the bottom of it. I read some people find it difficult to scrape clipped litter from the dimples on corners. They are not deep and we have not found a problem with cleaning it. Definitely would recommend.
Very pleased with this item. The depth along with the protective edge are perfect at stopping the litter going everywhere (my boy is one that likes to 'dig to China'!!) Oh and the edge/rim is easy to attach/detach and good at holding tray liners in place.