Although you can treat a two-row box as a one-row, or even two one-rows side by side, they are really different instruments.
A couple of local musicians who are not only top-notch one-row players but equally good on three-row boxes have told me that the bellows technique is quite different and that, because of the compact form of the one-row, balanced on the knee and with a thumb strap for the right hand, they use rhythmic effects that they just can't duplicate on a two- or three-row box. They use the right hand as well as the left to put life into the music.
So it seems to me that if you are going to play on one row, you could do more with a one-row box.
Conversely, a few Québécois players are starting to play on C#/D boxes, but it seems old habits die very hard and most of them play them solely on the D row. A big waste it seems to me. You've only got two duplicated notes on the outer row, but learning to use them judiciously makes a huge difference to your playing.
On a D/G you have more possibilities for cross-rowing and I would think that once you go beyond m*rris tunes

they are crying out to be exploited. Has anyone heard Tony Hall? The things he can do on a D/G are amazing - harmonies and counterpoint.
Around here the 3-rows in common use are ADG and GCF, and most players make excellent use of cross-rowing. Makes sense, because these are often quite heavy boxes!
And Brian, of all the 2-row diatonic systems to treat as a one-row, a B/C seems about the biggest waste....
