I own a solenoid piano( QRS Pianomation) with a pneumatic player
action installed in the same piano, and here is the differences I have
noticed.

Comparing the Standard player action to the Pianomation, the
Pianomation unit is very quick to turn the note 'on' but its a little
slow turning the note 'off'.  It doesn't 'bop' the keys, it is a solid
response.  For example a 'tah-dah' might end up sounding like 'tahhh'.
I don't think it's my piano; it does not have this problem with the
pneumatic action.  It is hardly noticeable, but it is there.

MIDI files any slower than 150 will enhance this problem with my
solenoid unit.  If I make the MIDI longer and speed up the tempo,
the problem is noticeably better.

Other than the slight delay in the notes turning off, I am very happy
with mine.  I have had it over a year, And outside of regulating it
when the new felts packed down, I have had zero problems with it, and
it gets played everyday, when I edit my MIDI files.  Cutting slots in
the keybed is pretty hairy to install it though, but when that is done,
the rest of it is a breeze.

Would I buy another Pianomation unit?  You betcha!  Performance equal
to a pneumatic system?  Very close.

Best Regards
Andy & Chris Taylor, Tempola Music Rolls
http://home.swbell.net/tempola/index.htm

 [ What music rolls did you use for the comparison, Andy?  Were they
 [ Tempola titles?  Could you supply the rolls and the corresponding
 [ MIDI files to other folks for their evaluation?  -- Robbie