Hi Jack.
I downloaded some music from your web site (http://www.campin.me.uk/Flute/Webrelease/Flute/04March/04March.htm) - "To Ballance a Straw" and "The Miller of Drone".
I downloaded the Tall and the Wide versions of the .gif files. I also ran the ABC for The Miller of Drone through Jon Freeman's Folkinfo "ABC Converter, and saved the result as as A4 PDF file. On the PDF, the music prints as two lines of music at the upper half of a page.

First impression of Mobilesheets on a 7" Android tablet.

Once I had copied the music image files onto the Android, I opened the Mobilesheets App. Loading music was easy - a standard file selection menu. You can put several of the image files together as a "song" - essentially as pages you can turn. You can't at present load a PDF in the same song as a .gif page.
Once loaded, you can display the music pages. When you load a song, it starts at the first "page". You can turn to the next page by tapping the right side of the touch screen.
You can zoom a .gif to a slightly higher magnification, but not (it would seem) a smaller one. A PDF zooms larger AND smaller (I think).

The images on the screen were readable when in Landscape view, but too small in a Portrait display. The "Wide" view fitted better.
The PDF view showed the two lines of music at the top of the page.

Additional features included being able to add a metronome beat (not sure how to control it).
You can also "Auto-scroll" your image. It starts after a couple of seconds and after a delay moved the page down two lines. I suspect the moving of lines was tied in to the number of metronome beats matching the number of bars in the image (but I could be just making that up).

I haven't looked at the more advanced file / songbook / music collection organising within the programme, but you seem to be able to organise by different criteria.

Quack!
Geoff.