Snoseal is actually bad for leather, as it works
into the leather fibers trapping dirt and grime,
literally breaking down the leather over time.
If you're using Lexol to clean and recondition
leather, a light coat of silicon (paste or liquid)
for water proofing would be better than a snoseal wax.

-- anything of

Egyptian style embalming?

*** Newsflash ***  "Neatsfoot Oil Good For Leather; contrary
                   research results expected at 11."

One has to decide what one wants: to use the bellows for
another 40-80 years or to set them on a museum shelf for 120.

Flexing dry leather will break it far faster than neatsfoot might
accelerate any 'rot'.

Going back to the Stanford U source [dedicated to preserving old
books], they describe a set of tests for leather preservation:

  The four dressings used were 1) vaseline, 2) neatsfoot oil
  and lanolin 60/40, 3) oil-and-tallow emulsion in water, and
  4) a mixture of lanolin, wax, castor oil, sodium stearate
  and water.

  The authors conclude that although the dressings provided
  some protection to all leathers, "their use was not adequate
  to prolong the life of the vegetable-tanned leather effectively."
  (They mention this because most leathers for bookbinding are
  vegetable-tanned.)

If bellows leather is not 'vegetable tanned' the dressing will
increase longevity, if it is then life will not be shortened.
At the least, do no harm.

  Analyzing the figures for these dressings ... [discard #1 & #4] ...
  neatsfoot oil and lanolin did make a difference. One finds that
  the leather treated with this dressing retained about 10% of the
  strength (as measured by slit tear) that it would otherwise have
  lost over the years, judging by the performance of the untreated
  samples. The oil-and-tallow dressing was about half as effective
  as the neatsfoot oil and lanolin.

From http://www.kb.nl/cons/leather/chapter2-en.html:

  At the British Museum HJ Plenderleith's study of leather
  dressings led him to develop the British Museum Leather
  Dressing which has since been used in many variations by
  conservators. The basic formula contains the following
  ingredients: 200 gram lanolin, 30 ml cedar oil, 15 gram
  beeswax, and 350 ml hexane. Sometimes 60% of the lanolin
  was replaced by neatsfoot oil.

'Real Men' use neatsfoot oil followed by SnoSeal (since Hubbard's
Grease is no longer available) and set the leather by the fire
for the wax and oil to penetrate the leather.  They dispense
with the Hexane, hand lotion and parfume, though a splash of
whisky now and then has been found to be anecdotally
beneficial.  

There are also formulas using lanolin, neatsfoot and 'oudorless kerosene'(?).

Neatsfoot oil is rendered from cattle bones and is a close cousin
to tallow.  The theory is to return the fat to the leather so
that it is 'lubricated'.  Lanolin is sheep oil.

Neatsfoot oil is also used on horses' hoofs.