I went to The Button Box website and had a look and saw the 2 Regals "G" & "C", the 2 Castagnari Melodeons both in "D", and the Melodie non Cajun tuning.
The Regals caught my attention because we all should know that Cajuns often bought them back in the day, but these seemed to be a knock off of the "Weltmeister", and they are in that dull flat black. Believe me, the lacquered black would be better for both looks and protection of the instrument's paint job. For what ever reason, these Regals are $400-500 dollars cheaper than the Weltmeisters go for. Maybe it's that the reeds in these Regals are of less value and quality compared to the reeds of the Weltmeister. Don't know for certain. Maybe someone else here knows why? The Regals sounded ok, but could have been better. Sort of cheapish.
But I had a look and listen to the 2 Castagnari's both in "D", and played my Gabbenelli Cajun King "D" along with the videos available for each. It didn't say if they were Cajun tuned, but I'm here to say that yes they are Cajun tuned, and a spot on match to my Gabbi King in sound and volume. Don't know how the Castagnaris would feel for proper play, but they are tuned right! Now, my Gabbi King "D" was special ordered by Greg Mouton of Mouton Accordions near Crowley, LA. I'm pretty sure, (because he mentioned it)that he had Gabbenelli put the better reeds available in it and ordered the accordion in shiny lacquered black. He also went over the tuning when it arrived and made sure it sounded older Cajun style.(similar to Nathan Abshire) and changed out all the strapping to match the "Cajun" preferred look. I say this because those Castagnaris sounded exactly like my Gabbi! And that's a got dam good sound if you know how to play it Cajun style! It will pass at any jam session, but you'll have to play loud by playing a lot of doubles licks to get above the 95 fiddlers and wannabe fiddlers playing along with you on your one accordion. Just FYI.
The Melodie accordion didn't have a video available for me to investigate it more... unfortunately.