These cages, based on an old French design from the '40s or early '50s, are possibly the best looking bottle cages of all time.
The Retro is a regular one-handed cage; you insert the bottle just like in any other cage, but it holds the bottle very securely due to the spring-like shape. You can spread the cage for an oversized bottle, or squeeze the cage inward for a better fit with a metal water bottle.
Retro cages are made by hand from a single length of 3mm stainless steel rod and then electro-polished. If you examine it closely from all angles you'll see that it is, indeed, hand made.
This cage with a tab on the back is made to hold smaller 18oz metal bottles and regular plastic bottles securely.