Extensive research consisting of frequent email exchanges with Paul Schwartz, numerous visits to Paul's web site, and contacts with dealers and makers led me to take a giant step and order a C&R Dipper Cotswold C/G tuned concertina. Colin Dipper recommended this concertina based on my expressed interest in playing slow tunes, such as traditional Irish slow airs, with chords.
The Cotswold is 6 1/4 inch across, whereas the smaller Dipper Clare model which is 5 5/8 inches. Cosmetically, the burr elm wood grain pattern blends nicely with the filigree ends, and the naval brass buttons and bellows papers further enhance its appearance. The Wheatstone button spacing allows me to easily reach some of the buttons that were a stretch on my Stagi.
The notes on the buttons follow the Jeffries system, shown in Bertram Levy's book, with three exceptions. The exception on the left hand side is the 31st button, which plays F#/E (same notes as left side buttons 12 and 9, respectively). It is located at the top of the C-row (when held in the playing position), next to the G/A button. I haven't used the F#/E button with tunes, but I expect to find it helpful with bellows direction. The other two exceptions are on the right hand side. The top button in the accidental row is a C#/C# (not D#/C#), and the button next to it is a F#/D# (not C#/D#). I find the C#/C# to be extremely useful. It makes playing tunes with this note easier, and more bellows friendly.
I took the concertina apart, and was very impressed with the internals of the action box. It's a mechanical masterpiece with shiny brass riveted action bars which move "frictionlessly". It has parallel reed pan construction with handmade steel reeds mounted in brass frames. The action is quick, smooth, and responsive. The notes speak immediately which attests to the quality and workmanship of the steel reeds.
It has a pleasant harmonious sound. Chords sound with a nice resonant effect. The resonant effect was an unexpected, pleasant surprise when I first heard it. Colin told me that this would get even better with time, as the instrument gets broken in. I am also pleased with the balance, e.g., the volume between the left hand and right hand notes.
Overall, I'm very impressed with all aspects of my Cotswold, but it's a Dipper so who wouldn't be.