More experiences collected at LHR in the last few days. Generally the HAL staff is well aware and trained to deal with people wearing the lanyard. I was proactively put at the front of the queue for immigration or security at T2 and T5, or when asked staff would do it without any issues.
Airline staff is more of a mixed bag: LH contracted staff knows nothing, BA gate agent knew and proactively gave me preboarding. On board BA one senior staff member knew what it was and checked on me a couple of times during the flight but not all were trained or recognised it.
Overall it is a positive experience and I recommend to get it If needed.