C. Robert Hopf Akkordzither Bag 100/3-4

Pro:
I asked Thomann for internal measurements, which they helpfully sent (see below) and find it fits my non-Hopf 74-string chord zither perfectly. There's about 1cm of soft padding, and the outside surface is some kind of leatherette.
It's expensive, but well made and it's the sort of minority instrument for which one can't easily get an off-the-shelf (nor even tailored-to-fit bag - which would cost much more than this did) - and I've tried!
It's just what I was looking for, to be smaller and so lower-profile as airline hand luggage (and much lighter) than the rectangular wooden hard case I made and normally carry my instrument in.
Delivery to the UK was very quick.
It's very convenient that it has a strap as well as a handle.

Con:
The only 'Con' is that I wonder how long the stitched attachment of the strap will last.

Here are the specs from Thomann. (My zither is slightly - perhaps 1cm - larger in length and width, but fits very snugly, which is just what I wanted).

Akkordzither Tasche 100/3-4
24 cm
41 cm
30 cm
53 cm
1kg

Width 1: 24cm
Width 2: 41cm
Length 1: 30cm
Length 2: 53cm
Heigth: 6,5cm

The weighting resulted in 1000g.