247, Q2, great confusion in AWO operations.
The original ICAO defined operational categories using DH and RVR have been eroded. First by the auto system integrity required by certification (CS-AWO; also CS 25); this is the aircraft - system capability which generally specifies min DH, sometimes rollout. More recently alternative equipments other than autopilots are used, also claiming credit for pilot manual control and training (OPS requirements); then depending on ground facilities, navigation source amongst other things, ….
Generally if ‘it’ can be proven to be safe then it can be used (can a human ever be sufficiently safe ?).
Thus less than 100ft DH has to encompass many systems and capabilities; however there is a step change in CS-AWO, 50ft, primarily integrity, combined with visual requirements - pilot cannot see enough to continue with a manual landing. Note; there are exceptions (beware exceptions) in RVR, e.g. 50 ft DH 150m RVR with ‘super’ fail passive autoland (as defined in the small print), allows manual reversion to land after AP failure in RVR above 200, but with RVR less than 200, a GA must be flown (e.g. AVRO RJ by modification and national approval).