Ouch! My neck! 
I prefer the strong-arm approach. 
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I can't stand any straps on my neck -- don't even like to wear my light-weight camera that way while trying to take pictures. I've never tried a neck-strap for my concertina, but, I don't think I will!
Of course, there can be many unique wrist and/or finger problems that are best treated by directly treating those specific areas.
The concertina is quite different from other instruments I've played (i.e., guitar), though, as far as how it affects my body. For one thing, there's so much of the activitiy/energy expended all down at the fingers, while my shoulders, upper arms and heart center, lungs, etc., are more still, and not quite all moving with the fingers. (I can't really breathe like I did with the guitar...though, that may be my own unique problem.)
So, I've almost felt like playing the concertina weakens my upper body muscles, because after I've played, they feel like they've been so restricted and just 'endured.'
It helps to do exercise that strengthens my arms and makes them feel more independent from the rest of me. This may sound odd, but, one of those 'Thigh Master' resistance gadgets, used more like an 'Arm Master' --- is great!! I've been trying that, lately. (Um...we won't mention my thighs, right now...

)
My heart's gotta pump or my fingers hurt more. Must keep my blood moving, down to the fingertips. That's another thing that suffers when I play the concertina, it seems. So, exercise certainly helps that.