I was mistaken about the layout of the Steve Baker Special (Hohner Marine Band 365 SBS): it replicates the low octave pattern, not the middle octave pattern, for the added bottom octave, and only adds 3 holes:

Cd Eg Gb | Cd Eg Gb | Cd Ef Ga bC | dE fG aC

This means that you do not have three (almost-)full diatonic octaves; rather, the gaps in the low octave remain. But on the plus side, you have instead two octaves with the low octave chording and characteristic low bends. Because of the gaps in both lower octaves, and the remaining gap in the top (requiring a tricky blow bend to fill), it's probably not a good choice for melodic work.