This is a "broad stroke" explanation of concertinas, the different keyboard layouts, reed types, and quality classifications. Its purpose is primarily to provide an elementary understanding of the differences between the available models.
Anglo
Each button plays a different note on 'pull' and 'push'.
keyboard:
Consists of 3 rows of 5 buttons per side. There are 2 layouts: Wheatstone and Jeffries.
pros:
Great for Irish Traditional and folkmusic. Easy to play simple tunes.
cons:
Partially chromatic, less suitable for more complex harmonies/ music.
use:
Primarily traditional music. (e.g. Irish, English, etc.)
English
Each button plays the same note on 'pull' and 'push'.
keyboard:
Consists of 4 rows per side, the middle 2 are the 'white', and the outer are the 'black keys'.
pros:
Fully chromatic, allows playing in all keys. The English can be used in all kinds of music.
cons:
Easy to learn simple melodies, but more difficult to learn at higher levels.
use:
Original classical repertoire, folk, ethnic, pop songs, jazz.....
Duet
each button plays the same note on 'pull' and 'push'.
keyboard:
The low notes are on the left side, and the treble notes on the right side, much like a piano.
pros:
Small duets are partly, large duets are fully chromatic, allows playing in most/all keys.
cons:
Easy to learn simple melodies, but harder to learn at higher music levels.
use:
Folk, pop songs, jazz, some classical.
Starter
reed type: hybrid
keyboard: Anglo, English, Duet
models: Jackie, Jack, Rochelle, Rochelle-2, and Elise.
Intermediate
reed type: hybrid
keyboard: Anglo, English, Duet
models: Minstrel, Troubadour, Busker, Clover, Peacock, and Rose.
Traditional
reed type: traditional
keyboard: Anglo, English, Duet
models: all Wakker models.