I bought the 3L cup for my rabbits! It's really good especially in the summer when they drink a lot more. It's annoying because it's not completely full and it's harder to fill it because of its big size. Very good! The problem I have is just with refilling water.
I really like this dispenser, for two main reasons: the non-slip bottom ensures my cats don't tip it over and the transparent container means you can see when the water is about to run out.
This water dispenser is great. It is filled from below. Should be kept clean from the inside (limescale deposits). If you understand how the dispenser works (pure physics), you know not to tip it over! The water runs out to the front if there is no water in the shell. So turn it round ;)
I bought the small size of 1.5L for my 15kg dog and it is perfect. At first it seemed too small but it has the perfect capacity for my dog, neither too much nor too little.