Apparently this was infamous for causing backfiring leading to the auto feather engaging so many crew didn't arm the auto feather.
Sounds like an Old Wives Tale. Flying the Convair 440 I have used ADI on hundreds of occasions. Not once did I experience back-firing on take off. Certainly we experienced occasional rough running due to spark plug fouling with 115/145 Octane fuel but it usually cleared itself during initial climb. As far as I recall autofeather was armed for every take off. .