[stumped]

as a final check on this format, i decided to check if the music scores would be extractable, as good quality images. seems they are. I downloaded the sample to K for PC, and calibre-converted the mobi to epub, then I could find the single page sample of music, and open it with picture manager
it looks to be a good quality jpg.
so one use for these ( still overpriced I think) books is as a source of hard to find printable music / tab for individual songs. without the stupid restrictions applied by sites that sell one-time-printable copies in scorch - where you get to try to print it once and only once - if you have a paper jam or spill coffee on it - tough..
arguably, ripping out the virtual "pages" from the kindle book , as jpg images, gives you more flexibility, as you can then crop, enlarge... or even just sellotape up to 3 pages together to lay across a music stand so you can play an entire song with no page turning