I haven't used one, but once I do get another phone I plan to. Seems it would help not only with mail, and menus but other things.

I use KNFB. It works really, really well for me. Fortunately, I got it as a Christmas gift last year though, because the price is otherwise pretty high. If you think you can get under them in price ($99USD) and provide similar functionality, go for it! There are other cheaper OCR apps out there, and I've tried many of them. But they just aren't as accurate. I'm not sure if that's because the OCR they use isn't as good, or because they're missing features like tilt guidance that help the blind user take the best photo possible.

I knew a guy who used one and it seemed to work well for him. Currently my only OCR experience has been on the Enhanced Vision Davinci CCTV system. I was super excited about it but it turned out to be not so great. It takes too long and I have to scan the same page multiple times, even at this it is sometimes annoyingly inaccurate so that feature goes unused now.

I use KNFB Reader fairly regularly, and it is the fastest and most accurate albeit The most expensive app out there for OCR. It can save multiple photos into an accessible PDF document although you do have to get used to taking the photo just right to get all the information.