It is (sadly) true that most American band organs (Wurlitzer et al) and
many German and French fairground organs lack any Celeste ranks.

The introduction of Bourdon and Flute celestes was part of Carl Frei's
radical reformulation of tone that led to the Dutch pierement sound.
(The other part was cutting back on reeds and mixtures and relying on
flutes and strings).

The Frei tone is warm and mellow, without being muddy or unclear.

Some makers of small "monkey" organs, such as Raffin and Deleika,
rely heavily on the Carl Frei concepts.  My Raffin 31/84 has only four
melody ranks, but one is a bourdon celeste, and no way would I be
without it!

I've heard some pretty big organs with the pre-Frei design, with
fascinating reeds and other effects but no solid foundation of bourdons
and celestes, and after a while their sound leaves me cold compared to
a Frei-based sound.

The celeste principal has a checkered history in church and concert
pipe organs.  Usually applied to soft string ranks, it is a hallmark of
all Romantic organs and is usually found in American church organs.

Neo-Baroque tracker-action purists frown on the Celeste, but very early
Italian church instruments actually had a second Principal or Open
Diapason celeste rank -- and the Diapason is the foundational organ
rank, the very epitome of Real Organ as opposed to orchestral or band
imitative stops.  So a Diapason Celeste is pretty radical by "modern"
thinking, but the Italians called it Voce Humana -- and it sounds more
like a lovely mezzo-soprano voice than the reed Vox Humana stop (which
itself is frowned on by purists, but which is actually a surviving
fossil of pre-Baroque organ voicing).

Church organ celeste ranks are usually mistuned just enough to give a
wavering, warm tone.  The upper harmonics of string-toned pipes then
warble at a much faster rate than the fundamental.

Monkey organ celestes, being stopped flute bourdons, are often mistuned
by 7 Hz or so, giving a very fast vibrato effect.  If these pipes had
more harmonics, the sound would be intolerable, like a rained-on piano,
but on the mostly fundamental flute sound it works.

Obviously each organ owner will tune the celeste to fit his/her tastes
-- so there's yet another reason why two "identical" organs will sound
different.

(By the way, small 20-note organs can be tuned in Meantone or Just
intonation rather than equal temperament, to get a more mellow sound.
I believe Meantone tuning is the basis for the peaceful, relaxing tone
of early music boxes.)

A pair of celest-ed ranks also sound louder than the same pair would
if tuned in perfect unison.  Each time the two sounds come into phase,
their amplitudes add and you get a peak +6 dB above a single pipe --
whereas two identical sounds added randomly give only an average of
+3 dB more.

A street organ without a celeste is like a person without a love life.
Or something like that....

Mike Knudsen