I also have an iPad Pro and have iGigbook and ForeScore on it. I find that both had shortcomings if you play jazz.
iGigbook is great as long as you don't annotate the charts on the fly. My band leader is often making changes to charts on the fly so it gets frustrating with iGigbook because you can fumble for minutes trying make edits when the rest of the band (using paper and pencil) is ready to go. What I like is that it otherwise handles compilation books really well -- and this is what most jazz players deal with all the time.
foreScore as mentioned previously has the editing part down much much better. But it has a really big flaw that prevents me from using it in any meaningful way in a jazz context. It assumes each pdf file is a different score. You can create a bookmark of a page within the book but you can't really treat that bookmark like a searchable tune and you can't have multiple bookmarks with the same name.
From what I've read on their forums, it looks like both developers are aware of their shortcomings but haven't managed to deliver improvements.
