This is the only bottle cage that will actually hold onto bottles in rough singletrack. They work best with the standard specialized bottles as the hook is designed to clip onto the top middle edge of the bottle. Be careful not to overtighten the bolts or you will dig into the soft plastic.
I really wanted to like these cages. I gave them months to loosen up a little bit, but no go. I feel like I am wrestling the cage to get my bottle out. So I drink even less than normal (and really, I should be hydrating better on my rides). Giving up now and replacing.