Hi Moyra,
I use the Brother QL 570 for my spine labels, barcodes and other labels and it's great.
I don't generate labels from Koha but the printer comes with a software package that enables you to set up the labels in the way that you'd like them to print. I just cut and paste from Koha for my spine labels and it's quick and easy. I keep a running spreadsheet of barcode alpha-numeric 'numbers' and the programme creates the barcode from each number.
The printer doesn't require ink and I've tested the labels by leaving them directly in the sun for a few weeks and they didn't fade or discolour. I don't know how they will go over time but we cover them with archive-quality label protectors which should help preserve the labels.
The best thing about the printer is that it cost me $50 and the refill rolls are inexpensive and last for a long time.
The printer would not be practical for a large library, but it is adequate for our small library.
Regards,
Deborah