Thanks for making this thread so interesting!
A lot of good points were made, and one of them can be summed up with this post and counter-post:
I suspect the real answer is that they all have their strengths and weaknesses, and whilst they might each favour being played in a particular way, in the hands of a good player almost anything is possible on any system.
Absolutely! But I caution that "almost anything" should mean "a style suited to any particular musical genre", and not "any particular arrangement of notes". Different keyboard layouts will often require different detailed arrangements in order to achieve similar "feelings".
The proof of this lies in the fact that (apart from a few "multi-concertinists") each of us has found a system that he or she can use to make the kind of music they like. In that respect, it seems to me less important how the real, existing assortment of small, polygonal bellows instruments came about, and more important how each of us made the decision for one system or the other.
Tied in with this is the frequent preferance for the term "familiar" over the term "logical" when comparing one's own ease of playing a given system vs. another system.
The question was put whether the Anglo, the EC and the various Duets should be lumped together under the generic term "concertina."
A good question indeed, because what makes two individual instruments qualify for the same name - e.g. mandolin - is the fact that a person who has learnt to play the one can immediately play the other without further tuition. And this is definitely not true of Anglo, EC and Duet. Not even of Maccann, Crane and Hayden duets!
Rüdiger (RAc) provided the key to this by pointing out that guitars are still guitars, even when they are re-tuned in such a way that all the fingering patterns change, and have to be re-learnt. The only significant difference between an EC and a Duet by the same maufacturer is, in fact, the "tuning", i.e. the allocation of fingering positions to notes.
Historically, the duet is a late arrival (I know, there was that early Wheatstone "Duett", but it took a while for Prof. Maccann to make a usable instrument of it!) With the German, the English and then the Anglo-German well established, what moved the Maccanns, Butterworths and Haydens of this world to add their duet layouts to the establshd hardware - and what led them to believe that there was a market for a new layout? They must have seen an added value somewhere!
Perhaps we have collectively found the answer to that.
Some of us admit to being unable to connect with the push-pull of the Anglo, with its constant search for alternate fingerings; others say they can't grasp the constantly changing roles of melody and accompaniment between the hands on the EC. The Duet can be perceived as a concertina lacking the "quirkiness" of the established systems (I'm sure we are all in agreement that the Anglo and the EC are each quirky in their own way, compared with pianos and guitars). In a way, of course, the Duets are quirky, too. You can't play a scale in a straight line from left pinkie to right pinkie, like on the Anglo (or the piano); and when you play fast, melodic passages in the treble your left hand can't assist your right, as it can on the EC (or piano). But somehow, I see these peculiarities as less quirky than the Anglo push-pull or the EC left-right.
In the end, the music-hall artistes proved the Maccann - and the Salvation Army the Crane/Triumph - to be useful instruments, and both were made in sufficient numbers to give us a wide choice of ways to produce that distinctive concertina sound.
Thanks for your contributons,