"A twelve hour dial is easily read at a glance, a 24 hour, not so
easy."
JS A 24 hour rotatable bezel with dark and light hours shaded as
Seiko has used for years is exceptionally easy to glance at and tell
whether the target zone is approaching evening, entering dawn, etc. It
takes no conversion of 24 to 12 hour time...just knowing dark means
dark, etc.

" and beset with problems such as lack of shock resistance"
JS Are you aware that for the past half century almost all
mechanical
watches use shock absorbtion devices like Kif or Diashock. Modern
mechanical movements are surprisingly robust. If the last new watch
you tried was in the 1940's, then I could understand why you might
make
such a statement.

"How many G's will such a device withstand?"
JS Well, since Omega sent it's chrono with a shock absorption
escapement to the moon several decades ago, I would estimate that it
would withstand several "G"s. And China's first astronaut wore a
mechanical chinese-made chrono into space recently. Actually the valuf
of Kif-like shock absorbers is mostly in absorbing sudden shock from
being banged or dropped.
I do have to ask...why are you asking about the number of G's a watch
could withstand...is there some relevance to keeping track of time for
swling or internatonal travel?