Small size, & cats stopped using it
I bought one of these two years ago because I liked the top entry design and overall look and solid build (if not the very hefty price tag...). All four cats tried it; one used it for a while fairly consistently when young, then all stopped using it given any other litterbox choice (and two refused to use it at all). I think the main problem is that the space inside is very small and cramped for many cats, especially larger toms. I just dragged it out again to try to get two new kittens to use it so that it wasn't a total waste of money. To me the key point was that given the choice of several types of boxes in the house, cats preferred other form factors and not this (even when it was swapped around by location). I'd consider a larger and lengthier shape but to be honest, for a fraction of the cost it's easy to do a hack with a storage box and lid, with an opening cut in the lid... wish the cats had liked the box more as it is attractive in a world of ugly litter boxes.