As is the case with so many building components, the component or system is only as good as the way in which it has been installed. Frost-free hose bibbs are a great idea. The valve actually shuts-off back in the wall. So when the faucet is turned off, the water near the outside drains out the front spout of the hose bibb, assuming it has been installed/sloped correctly. Therefore, any water left in the hose bibb is retained back in the warmer crawl space or basement area.
People have ways of messing up hose bibbs so, despite the clever design, they do not work. Here is such an example. This hose bibb, by homeowner efforts, has been converted into a permanent underground watering system. When it is turned off, water stays in that flex tubing and that makes the hose bibb just as susceptible to rupture as any other hose bibb.
This is another example of a homeowner design that ends up creating potential problems that did not exist in the first place. A much more common way to mess one up, that so many people are guilty of, is to simply leave the garden hose on the hose bibb in freezing weather.
Check out "This Day In History" -- music and vintage television from the 1950's through the 1980's. I enjoy writing these articles because they take me back to my days in radio broadcasting. Click on Elvis' gold record, below, to revisit those golden hits of yesteryear.