The design of this simple object has stood the test of time and seen minimal changes or alternatives. I consider this to be an example of good design for a number of reasons.
Firstly, using the keyring is intuitive as the user can quickly see how it works simply by looking at it. It is also versatile, for example, multiple keyrings can be very strong when linked together.
Keys cannot fall off when attached as with some alternative clasps which do not fully close and it is made to be as robust as possible by being made from one piece of metal. This eliminates the potential for parts to fall off or break.
It is hard to bend out of shape as the circular overlapping design gives it strength and anything with a hole or loop can be attached, including various materials for either practical or decorative reasons.