Anglo concertinas play a different note on the push and pull of the bellows. Lower notes are on the left-hand end; higher notes, on the right-hand end.
20-Button Anglo Concertina
A 20-button Anglo concertina has 2 rows of buttons. Half of the 10 buttons of the inner row are on the left side and half on the right; ditto the 10 buttons of the outer row. Don’t be confused by the 21st button, which isn’t usually in a row at all but somewhere near the right-side handrest. That’s the air button. Instead of playing a note, it allows you to open or close the bellows quietly.
Each row of buttons is in a different key, most often C and G, although the lower-pitched combination of G and D is also common. A 20-button concertina can play nicely in its home keys and their relative minors. If your vision is playing tunes on your front porch or by your campfire and you’re not concerned about playing with other instruments, a 20-button concertina might work for you just fine.
30-Button Anglo Concertina
A 30-button concertina adds a row of accidentals to the two rows that are in specific keys. Although it isn’t completely chromatic throughout its range, a 30-button instrument will play comfortably in several keys beyond the home keys. If you will be playing with others or think you might someday, getting a 30-button model is a good idea.
The non-linear button near your right thumb is an air release.
A Word on Custom Layouts
Although radical changes to the tried and true are not always feasible and not typically advisable, some modifications are fairly common. For instance, people getting instruments made to order with the Wheatstone layout sometimes replace the d# on the push on the first button of the right-hand accidental row with a c#, thereby gaining a c# in both directions on a button that’s easy to reach, and in a useful range–the octave above middle c–too.
R. Morse & Co. Ceili Anglo Concertina, inside and out.