Talking of which, cam anyone explain to me why a lot of Irish concertina players choose a C/G when a G/D does the job without using the accidentsls?

Quite simply, this was because C/G was by far the most common for anglo concertinas. Older players played up and down the rows, and because it was mainly played in the home it didn't matter that they couldn't join in with other instruments. Then the modern cross-row style was developed to play in the fiddle keys. This forces the ornamentation to be played in a certain way. Whilst it might be easier to play the tunes on a G/D, critics say that the essence of the style is then lost. Despite the now wider availability of instruments in other keys, the Irish style is built around the C/G.