I've seen these are still sold by Hal Leonard, even if I understood their conception is old. From the ad there isn't quite clear what they really are.

How good and effective are they today as didactics, compared to modern methods like Faber or Bastien ? Are they optimized only to teach beginners given easy songs, or are they teaching general-purpose reading enough to play, say Bach ?

Is their contents, arrangement style etc. specifically suited to organ, as compared to piano ? e.g. I found the arrangements in Faber quite 'pianistic' in that pieces sound nicer with the attack 'ping' and decay of piano than on a bland 'organ' or 'flute' sound.