BFO- Beat frequency oscillator. Not required in the UK but I am told it was required to ident NDB's in France.
BFO is required to hear any A1 signal as it has no modulation and therefore no tone, unless it has something to beat against.
Being used to a "normal" ADF with a digital output
There is no ADF in the World with a digital output! It may have a numeric display, but so does the tuneable one where 300 = 300 and 11 = 1100. Don't people learn to use rulers any more?