Both these instruments seem well suited for traditional and contempororary folk song accompaniment, although the[ more modern] concertina seems to be associated, more with trad music, than contemporary.
Both seem to have advantages and disadvantages,the guitar can be more difficult to play without imposing rhythym[ to play freely].The concertina has advantages that it is not susceptible [tuning wise]to temperature changes, but has none of the sympathetic ringin strings advantage of the guitar.
Im assuming that the majority of mudcatters prefer the guitar[ I like them both], I would be interested to hear mudcatters preferences for song accompaniment,[andwhy] please vote for concertina or guItar or both. Dick Miles