Hi,
on Christmas Day I got a new whistle - Caillagh low whistle D.
This is my very first recording: Inisheer

(actually, I bought it a month ago, but I had to wait until I find it under the christmas tree. Nevertheless although I choose it, it seems nothing is perfect and I have to return it and choose another one. Perhaps, at first I ask my teacher whether problem is on my side or on whistle side)

I don't remember if it was the first one or the second one.
The first one had main (and big) problem with leaking air in the fipple.
The second one had various little problems, but after I hear it how plays in teacher's hands, it seems there is only one small problem - weak bell note (which is common to all Caillagh low whistles and not only Caillagh whistles).
Everything other problems was more on my side than whistle side. In short, low whistle is not same as (soprano) whistle :-).
This is my first low whistle I held and I was surprised how unwillingly jumping from higher octave to lower octave, how wide is "forbidden" zone between octaves compared to soprano whistle and I expected that low whistle has more backpressure.
Simply most of problems are ... behaviour than problems.