> In (phonological) practice, this means that you can now use /&/ to denote
> any mid-central vowel, even if its main allophone is rounded (French,
> Dutch). The other symbols need only be used if there is more than one
> mid-central vowel (for instance a more open vs. a more closed one /&*/ ~
> /3/, or a rounded vs. an unrounded one /&*/ ~ /8/).
To illustrate this with concrete examples from non-rhotic accents of
English, the quality of the vowel of <bird> is [@\] (= Miguel's [&*]) or
even [I\] in Australian,  in RP, often something ranging between
[9_"] and  in London Cockney, and between [2\] and  in New Zealand
English. But in phonological practice /3/ is clearly pref/3:/ed over any
of the other symbols unless we have a particulat reason to use a narrow
phonetic transcription (e.g. when contrasting one accent with another).
My personal preference is to use /3/ for a "full" vowel (one that has a
well-defined phonological target in the mid-central area) and /@/ for a
"reduced" vowel (whose quality will normally be far more variable).