I used to have a Eversweet 2 and recently purchased Eversweet 3 for my 2YO ragdoll. Here are some things I'd have found helpful before making my decision:

+ It has a 7 day backup reserve powered by 5 AAA.
- The AAAs need to be inserted after removing a tiny screw at the bottom - need a watchmaker screwdriver for this
+ Really intuitive design in terms of refilling and cleaning. No foam piece to wash or long plastic detachable pipes.
- No waster level indicator to show you ~ how much your catoo has had (does have a refill light though but that's a separate use case)
+ Uses a USB cable which can be replaced if it brealks/ stops working (need to buy a new one because the old one's power wire went bust!)
- Does not come with a wall socket (they are trying to be environmentally friendly, which is appreciated)
+ Catoo loves it! Watches it endlessly and sleeps next to it (sounds softer than Eversweet 2)