Time mechanical fuzes are both hard to manufacture and have a much greater failure rate than either Time Combustion or more modern Electronic Time Fuzes (ETF). They also have the added problem for us of being the single most dangerous type of blind you can get. A single piece of grit can stop the mechanism and movement of any type can restart it (which is a bad thing)!! Another reason why the disturbing of shell whilst on the battlefields is not advised.
Fortunately the manufacture of them especially during the wartime conditions was so difficult that they were not in great use but enough still exist that they do crop up occasionally. Talking to the de-mineur these are one of the only items that they 'Blow in Situ' without exception.
As centurion says the AA use of ETF or Proximity fuzes came about at the end of WW2. The British had a Top Secret project at the time called Green Archer which was the protection of London using radar controlled guns and Prox Fuzes.
The modern criteria is that at least three separate safety arrangements are in place in the fuze up to the point of firing. During WW1 at least two were in place even for such dangerous fuzes as the Hotchkiss base fuze (6 Pdr tank gun) (a lead shear strip and a creep spring). The usual set back, centrafugal force, set forwards and mechanical safety (such as clockwork) were all used and actually the fuzes were very safe, (for the period), with any mk's or Models that proved problematic being withdrawn and replaced in short order.
P.S. Time mechanical scares the Cr*p out of me, I hate dealing with them
!! Oh and Hotchkiss have the same effect !!!!!