The pee-poo separation doesn't work so save your money and get the "essential" model instead.
I purchased their "pro" model with the pee-poo separation feature. The separation system really doesn't work. The slope of the grate isn't steep enough to get the poops to roll down it, hay easily falls through the upper grate and quickly blocks the poo ramp anyway, and pee still ends up in the poo tray at the bottom sometimes (if the bunnies pee near that end of the little box). It's also much harder to clean the pee-poo separation grate since hay gets stuck in the tiny openings and has to be removed by hand - spraying it down with water isn't enough to dislodge the hay. The ramp is poorly designed as well. It has two tiny nubs that connect it to the litterbox but they're way too small and the bunnies inadvertently knock it loose all the time. Luckily my bunnies are big enough and healthy enough to just jump up and don't really need the ramp. I do like the quality of the basin and the top grate, but I really wish I had saved the $65 and gotten the cheaper model since none of the fancy features of the "pro" even work.