Most all of our cages have the top fill, and we love them. I do have some of the roller ball ones that I use in the quarantine cages. If we get some rabbits that are more used to crocks, and can't figure out the top fill bottles, I transition them to the top fill using the roller ball bottles. I find the top fills so much easier to fill, and scrub out also. Take the top off, and a couple swishes with the bottle brush, and it's clean. If I were comparing the top fill to the roller ball bottles, my rabbits that use the top fill drink way more water than the ones that use the roller ball bottles! WAY more! They can lick and lick and lick on those, and they just don't get as much as they do from the top fills.