That works fine, as long as the name does not have any spaces or punctuation in it, but I would always recommend putting that in single quotes:
diskutil unmount '/Volumes/Freebird'
It won’t hurt anything if used when not needed, but getting in the habit of quoting paths when doing anything in shell will be a good habit to have.
(If you are using a variable such as $HOME then you need "double quotes" but that does not apply here.)