It's not me, it's you

[Chris Ghent]

The best advice to give anyone is try it first but leaving aside your particular difficulties it is hard to know whether you are playing a good instrument when you are inexperienced. If you find your playing improves immediately then it probably is better than what you have been playing.
 

It is best not to look closely at a concertina before trying it; they are often so attractive you will want to own it and may miss any operational shortcomings.  

 

If you are after an intermediate concertina one I can recommend is the Morse.  This is not to disparage any other concertina, I have never seen a Minstrel for example. The thing is, every Morse I have had anything to do with has been exactly the same, which leads me to recommend them with confidence.   They made about 1000 of them and most are probably in the US. They are reliable and work very well. I know at least 5 people locally who have bought second hand ones, mostly from the US, and all are very happy with them.