We currently have four always indoors cats, we have had as many as six at one time.  We have owned as many as two Litter Maids at one time and experienced the same problem with all of them.  First the solid waste sticks to the forks and is difficult to clean.  Second the trays are expensive and messy to change.  I see where they are now giving you 18 trays for about the same price we were paying for twelve, but at over $1.00 each they are still too much.