Great quality, poor dispensing volume
I bought 2 bottles since you're supposed to keep a spare in case something happens to one. Thought I'd try 2 different ones, see how they compare.
I bought this glass bottle, and the Ferplast Drinky Water Bottle.
This bottle feels very high quality, being made out of glass, and the gripping capability of the hooked spring that sits in a groove near the bottle "top" (sealed base, opposite of dropper end) is excellent.
However, the dropper end has a relatively small ball bearing and narrow tube, meaning the amount of water dispensed per "use" is less than you'd hope, which makes life difficult for my guinea pigs. Also, the dropper tube is very long which is disadvantageous for certain cages such as mine where the bottle must be attached at ground level. This is because the longer the dropper, the closer to the ground the ball bearing is, and the more your pet must twist its neck to drink from it.
The Ferplast Drinky I ordered holds more water (600ml). The bottle is made out of cheap looking plastic, nowhere near as high quality as this glass one, BUT the dropper is short and stubby with a fat ball bearing, which is much, much better for my piggies! It comes with a wire-cage-only attachment (one of those plastic twist-lock slot attachments) so I used the spring hook attachment from this glass bottle with it instead; even without the groove on the bottle the spring's tightly holding the bottle into place.
The Ferplast, although cheaper looking, dispenses far more water per "use", so I must recommend it over this one.