Hi Tunborough
Seeing as you dropped me in it
I have the low D with aluminium tubing. I got it from eBay, as per normal. It definitely looks the part, if nothing else.
It is incredibly light for it's size, the person I bought it from had ordered it with offset tone holes and as the previous poster said, the bottom tone hole is way lower than a normal low D. Playing it required the use of the little finger on the bottom hand, but it was playable that way. Getting the key from the seller as a separate purchase meant that normal fingering was possible. (If you buy the low D make sure you get the key as well).
I am still getting used to playing it, so this is an initial impression. It has a very breathy tone when playing it in the 1st octave, the second octave is purer, but is easy to overblow when in the second octave - no doubt as I adapt to the instrument's quirks it will play better for me.
David