Overall, I really like this box.  The gel litter is amazing at absorbing urine, eliminating odors, and cutting down on the tracking of litter across the floor.  For all of these reasons, I am beyond thrilled.
The except.....has to do with the disposable tray.  Purchasing a replacement disposable tray with litter is double the price of just purchasing the gel litter.  And the tray is truly disposable since it appears to be made of wax paper.  I will normally recycle even the disposable, but in this case, that isn't really an option.  Purchasing the optional, reusable (solid plastic) tray is highway robbery, but I did anyway.
My review would have been 5+ stars, but detracting one for the pricy reusable tray that really should have been included