Yes, it was "limited service" on the Western Front indeed: limited to scouts and snipers. The vast majority of P.14s seem to have sat in store with many, perhaps most, sold off during the 1920s and 30s. Some definitely ended up in India, as did many Ross MkIIIs.
One Dr. Common designed during and just after the Boer War what was for the time a very advanced optical sight for the Lee Enfield which IDS illustrates in his books. Needless to say it was not adopted by the War Office! There is at least one example in the Pattern Room Collection. Short tube, external adjustments, large range dial easily viewed from firing position etc. All features that would be "re-discovered" decades later, but then Dr. Common was a self-taught "amateur". ;)
There was another advanced optical sight designed by Sir Howard Grubb around the same time, which is detailed here.
One wonders whether Grubb's work inspired other prismatic sight designs, such as Goerz and Zeiss? That article dates to March, 1901. This would appear to be the first optical sight that allows bifocal use (both eyes open) and therefore predates the Zeiss bifocal of WWI, although the latter was the first true "long eye relief" scope AFAIK.