The question was raised about movement size vs. case size.  I would
first say that you'll never see this in the older movements, just the
later mass produced machines.

First of all, I don't find them aesthetically appeasing, but if you
close the lid and listen to the music, you may forgive this defect.
What's important in any music box is the music it plays.  If you find
the music pleasing, it may be a good box to buy for you.  Not everyone
wants to invest in excess of $10k to buy a Nicole Overture box.

How do you tell a high quality movement?  Unless the makers name is
stamped on the bedplate or some other trademark is visible (which is
indeed rare), you cannot be sure of who made the box.  A few signs
I look at are (a) the spacing of the teeth in the comb, the simplicity
of the design, if the inlay on top is wood or other inlaid materials or
a decal and the general construction of the box.

There's a minimum spacing that the makers could use for spacing the
pins in the cylinder (I don't remember the width right now) but in
general if you have two boxes with the same number of tunes, the one
that has a finer spacing between teeth was probably a better box to
begin with.  If the box has an elaborate tune card, it's probably a
lower quality box.  Clean straight lines indicate a higher quality box.

As for the construction of the box, a few of the corner joints on my
keywound boxes are so interesting, I have no idea how they put it
together.  It makes the box very rugged and practically impossible to
take apart, another sign of a good box.  I have seen a low quality box
that didn't even use any form of joining -- just a simple match with
glue and nails.

I have purchased several in the past that I've no idea what the music
is supposed to be.  (Right now I have three in line for repinning the
cylinder and possibly a fourth that I should receive very soon).  If
you consider buying a box that needs to have the cylinder re-pinned,
remember that you're adding a considerable cost to the investment --
somewhere in the neighborhood of around $600-$1000 depending on the
size of the cylinder.  If the box is worth the expense then go for it.

When I listen to a music box to decide whether to purchase it or not,
I generally like to play it without spring pressure so I can
concentrate on the tone of the individual notes and chords without
being interrupted by the next.  A well aligned comb should be strong
enough to hear, yet gentle enough that it's not over-plucked.  A chord
played should continue to vibrate several seconds after the chord was
played, and it should have sympathetic vibrations from the surrounding
teeth which you can actually hear.

Eliyahu Shahar