The one-row melodeon is probably the easiest to make sense of playing only a diatonic push-pull scale in one key. Most have only 2 bass buttons or spoon basses, Hohner did make some one-row pokerwork models which had 4 basses.

STANDARD ONE ROW MELODEON LAYOUTS
• C
• D
• G
• A
• Bb

HOHNER POKERWORK ONE ROW WITH 4 BASS BUTTONS
• C
• D
• G

I think these were the only keys Hohner made this model in.