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 (for instance) 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 is "Type I", with no tab, which is the traditional design.