I have been following the recent group of articles about Aeolian's
Metrostyle, and thought I would add in my own two cents. When I bought
my 1913 Steinway Foot-Pumper, it came with a number of Metro Art Rolls.
These rolls are hand played, yet have a Metrostyle line. On each leader,
there is a box of words printed in red ink and it says the following:
(I have been careful to copy the original spelling and punctuation)

The Value of the Metrostyle

The only objection that can be made to recorded rolls is that they
always play with the same tempo, and no matter how excellent an
interpretation may be, it becomes monotonous if never varied. It is
extremely difficult for an unskilled performer to correctly alter the
tempo of one of these rolls; indeed, it is almost impossible, unless the
changes are properly indicated on the roll itself. This cannot be done
except means of the Metrostyle line. This line provides an authoritative
interpretation which can be followed exactly or used in part as a guide
to individual interpretation

Right next to those red-ink words is another box, this time printed in
blue ink

   The Metro Art Rolls

Are reproduced from the recorded performances of expert pianists and
they portray with wonderful fidelity the distinctive characteristics of
hand-playing.

Augmented by the Themodist, Graduated Accompaniment, Automatic
Sustaining Pedal and The METROSTYLE, Metro-art rolls enable the
performer on the Pianola to render a Composition in a manner closely
approximating the most artistic keyboard renditions.

I also have an Aeolian Uni Record roll, which does not have a
Metrostyle line, but it does have the following words printed on the
leader in black ink:

   The Uni-Record Rolls

Are the recorded performances of hand playing and they reproduce with
every accuracy and feeling the individual playing of each performer.

Uni-record rolls are NOT an Arbitrary interpretation, they record in
each roll the playing of one particular Artist, but allow the player
performer to alter the tempo as freely as he may desire.

Finally, let me say that in early Aeolian catalogues, they list the
artists who have made Metrostyle rolls. Among the names are Nicholas
Rimsky-Korsakov and Issac Albeniz. Has anybody ever seen these rolls?