A few years ago I had the same dilemma as you - I upgraded to an A.P. James in 2018, & I liked it. It was consistent & played faster than my previous concertina, which was important as I play Irish trad. It was loud, which can be helpful if you want to hear yourself in a session. Also it never had repair issues.
I upgraded again in 2020 - a second-hand Lachenal from Barleycorn. It plays even faster &, now that I have concertina reeds, I wouldn't want to return to the A.P. James with its accordion reeds. Although there have been repair issues (some unresolved), I have no regrets. You might say that I should have bought a Lachenal in 2018, but two years of playing the A.P. James really clarified in my mind what I wanted or needed.
I spent an afternoon at Barleycorn in 2020 & I would recommend a visit. It was a bit embarrassing for Chris to hear my terrible playing but, after two hours of trying instruments, I forgot that he was there (having a friend with me helped my confidence, but you need a very patient & tolerant friend!). I must have tried about 12 different instruments, some two or three times. You're dependent on the stock there, but you probably can't find a better range anywhere.