"If you have ever struggled with securing a water bottle with or without that flimsy metal hook they come with (my favorite was jury-rigging a rubber band at the bottom of the bottle base, stretching it up outside the cage and hooking it over the top of the bottle), these things are great. the metal hook on the back makes for a secure hold, the metal springs and bottle holder band keep the bottle in place and even allow for a little height adjustment, if you can't use a different rung on your cage."