Drifting slightly away from concertinas to accordions... I once saw a very talented guy play a Classical Piano Accordion Repertoire - on a (I think 3 row) Button Accordion! And if you had your eyes closed, you would be hard put to tell! And the fledgling button box player sitting next to me 'just didn't like the music', and didn't realise just how good a player he was!

It IS possible to mimic the 'Anglo Style' on an 'English Box', but you will need to move the bellows in the same physical way that an 'Anglo Player' would, and not the natural way a normal 'English Player' would, in order to get the same 'legato, or lack of it' rhythmic style.

And as for starting - you learn 'music' & 'music theory' (including 'reading the dots') on your first instrument,as well as learning the physical technique, no matter what it is - for all subsequent instruments, you are just mainly struggling with the physical technique of the instrument itself.

So if you only really plan to want to play only one instrument, then get the one you want to start to work on.

I was lucky - my Duet came with wrist straps. Any serious (ie used it a lot!) player would most likely have fitted them to any vintage instrument when they were originally 'new', so most boxes that don't have them now, were probably not used very much.