"All Russian Extraordinary Commission for combatting counterrevolution, sabotage and speculation", short for Cheka was founded on December 20th 1917 and the forerunner to KGB. OGPU, short for "United Government Political Administration" replaced the Cheka in the 1920-ies, which was then replaced by the KGB.
The content was usually of political, economical, or administrative nature, and hence of little military interest. On occasion, messages dealing with troop movements, crossing of rivers etc. had been intercepted, which may indicate that this cipher system is used by some of the army stations, or that the Cheka stations at times relay army traffic.