I liked forScore, but never tried MobileSheets. I’m a retired musician with a growing pitch perception hearing problem, possibly the weirdest I could’ve ever imagined, so I’ve dropped out of performing. (Couldn’t find any hearing aids that wouldn’t distort when a blaring trombone bell was necessarily close to my head. I still play some, but only when others can’t hear me, and while staring constantly at a tuner.) But the reason I’m posting is to contribute a 3D printing design I created for turning a $20 wireless calculator into a page turner for my iPad. I made a neat little Youtube video that gives detailed instructions for the setup. Thought you might get a kick out of it even if you don’t find it very practical. Here are both links.
I wish I could provide that kind of answer, because you deserve to have one. However, because my perspective is one of hobbyist, I’m afraid doing so would entail as much research for me as it would for you. I once tried to make such a purchase, and was directed to other hobbyists, and although I made a friend and got a really cheap 3D print out of it, I didn’t make any progress toward establishing any commercially viable affiliations. That’s why I mentioned practicality in my first post. It probably wouldn’t be practical to entertain involvement with an open source project like this unless you either have a 3D printer hobbyist friend or are interested in becoming one yourself. I think that some of us (younger than me) may look forward to the point in history when 3D printers reach the same level of ubiquity attained by vacuum cleaners and microwave ovens during the previous century.