Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Large & Small models are awful!

I have both the large & small models. The small one works better than the large. Neither work well and it is almost easier to go back to a manual box. Their lack of performance have caused me to look again for another self cleaning litter box. The two are messy and mut be emptied every 2 days. The larger one does not even get its "load" into the tray. Do not buy either one!