I have a pair of D/G instruments (one by Bob, one by the Dippers), G in the middle, D as the inner row but down a 4th rather than up a fifth..
The biggest challenge (other than the lack of instructional materials) for an Irish sound is that you can very easily play very long runs in one direction across the rows, which gives less of a bounce than Irish concertina tends to have.
Oh, and you have to commission the instruments separately, and you can't really play other peoples' instruments. The enforced quasi-immunity to Gear Acquisition Syndrome may be construed as a benefit in some circles.