Thanks a lot - all good info. On that last point - I have been playing various instruments all my life and conclusion was always the same - you outgrow the very basic model fast and then it is a frustration, attempts to sell it etc. So on beginners intrument it makes sense to buy used with some ability to check it. But market for concertinas is not huge - either way - like e.g. for cheap bass guitar. So buy better quality new and then keeping it for few years until it starts slowing you down was always my way. With guitar it would different - market is big and I know exactly how to judge used guitar - so I did not buy new guitar in decades.
I am still on the cusp - not sure if I want concertina or button accordion - the price is about the same but I was told accordion is a bit easier on hands - and prices for midrange accordion at McNeela and Phoenix are comparable. Main argument for concertina is compacthess - seems like a better instrument to travel with than button accordion.
Edit: Friend of mine let me borrowed his cheap piano accordion - so now I have some ability to get familiar with the ergonomics of the instrument. I wanted to play flute long time ago and I borrowed one and it turned out I could not play it without instant shoulder pain so that was it. Don't expect that with accordion but want to learn few simple tunes and see if there is "need to play is as much as possible" feel I usually get from guitar.