Plus, there are other, less intrusive way to achieve "show the available valid
key bindings", such as the which-key package.
As I mentioned in a recent response to Stefan in this thread, I did a poor job with that problem statement.. I don't want to *just* show the available bindings.
I think one area where Hydras come into their own is that once you have the
Hydra active, it stays active, allowing you to chain together many single-
letter commands.
That's correct. It's up to the package author as to how much of hydra features they want to pack into their package's hydras. hydra is not *just* for showing available keys and/or *just* for chaining many single letter commands. It's much more, in a good way.