iOS has pretty decent built-in OCR and TTS but give it a try on a book page if you're curious — unfortunately the OCR makes a lot of mistakes (as well as including footnotes etc.) and the TTS is still pretty robotic. I do hope and expect they'll improve soon, though, at which point the only advantage of this app will be that it can scan multiple pages at a time — probably not enough of an advantage to justify its existence at that point although I'll see what users say. For now, as far as I've seen it's the highest-quality option for this (granted, very niche) paper-to-audio use case.
Also Azure actually! Yeah for a sentence or two the onboard OCR usually gets it right, but if you’re listening to a few pages at a time there are almost always a bunch of errors and it gets pretty exasperating to listen to.