I've tried them all. I like these the best mounted on the outside of the cage.
I've never had any problems with predators but my cages are raised and also inside a fenced area with chicken wire on top. You could mount them on the inside if you don't want to cut a hole in your cages.
I use a similar cup from GQF and I have them inside the cages. Mine don't fill with water, they just dribble out when the quail pecks at the lever. I've got 1 cup in each cage and most cages have 7-8 birds. Some have more and some have fewer. Doesn't seem to be a problem with them getting enough water. When I feed and collect eggs, I'll finger the lever and fill up the cups so the birds can get a big gulp.
Never had one fail, but recently one got some trash or something up in the spring and it just kept running water. Took it apart and cleaned it out and it works fine now.
I even use them in the brooder boxes once the quail are a couple of weeks old.
I've never had one fail yet, mine are hooked up to a low pressure system so I don't have to refill a bucket. I only have one per cage and I have 6 or 7 birds in each cage.