I wonder if alr install should honor the XDG Base Directory Specification:

User-specific executable files may be stored in $HOME/.local/bin. Distributions should ensure this directory shows up in the UNIX $PATH environment variable, at an appropriate place.

It doesn't sound very mandatory, but that will make the installed programs directly visible, at least on most Linux distributions.

Was this considered? It's just a minor matter, though, since the prefix can be freely specified.

Two other comments about the prefix:

Can't the prefix be configured, only specified on the command line?

alr install --help
[...]
   --prefix=ARG  Override installation prefix (default is ${CRATE_ROOT}/alire/prefix))

Shouldn't it say that the default is ${HOME}/.alire as in the DESCRIPTION?