The English Concertina and and the Anglo
The first is unisonic, the Anglo is Bisonic.
They are two completely different instruments as different musically as a diatonic harmonica to a chromatic harmonica.
[whilst the Ango is fully chromatic 30 buttons upwards], its sytems of embellishments by its nature is very different from the English Concertina, players of the chromatic harmonica often employ different, forms of ornamentation to diatonic players, some play it as it was designed to be played in orthodox chromatic fashion, some play it like a diatonic in its home key using the slide to provide ornaments, the effects are very different from a diatonic harmonica.
The Duet concertina is also unisonic, it has an octave overlap left and right which can be useful for playing in a linear style, quality concertinas are often available at cheaper prices due to lack of popularity mainly because a lot of people are advised by their teachers that the Anglo is the best system, the disadavantage of the unisonic sytem is its lack of natural inbuilt rhythm can be overcome by changing bellows direction more frequently, for example irish polkas can be made more
rhythmical by changing bellows after every crotchet, or paired quavers,
jigs by changing either where one would tap foot, on first or occasionally fourth beats, variety within these systems can be obtained by occasionally breaking the pattern and in particular including lead in notes of phrases,and by reversing bellows at end of phrases this helps to prevent the sound from becoming predictable. the advantage of unisonic concertina becomes apparent when playing slow airs, where the player does not ruin the flow of the tune by a sudden reversal of bellows.
using a system like this can also be useful for playing Morris tunes, where more frequent reversal of bellows can provide the rythym needed for morris dancing, in fact is perfectly possible and is an interesting exercise to take a tune like young collins, and play it as an anglo player would using similiar reversals, or alternatively reversing after every 2 beats and occasionally every beat and at end of phrases.
st patricks day which is an irish jig and is closely related to a morris tune is an interesting one I have found is in my opinion fun to experiment with.