Well I suggest you use JTtalk. It depends what your target crowd is, because legally blind and what you may think is blind can differ and not everyone knows Braille. The benefits I saw of Jtalk really relied on the examples it had, and how well they worked. To do our entire front-end part of the project with JTalk only took us 2 days, because we pretty much just edited the examples it had. Speak.js had a more difficult learning curve in my/my group's opinion. However, we found that the speech was a bit slurred and had comprehension issues, especially for documents where there were a lot of names (example stock articles mentioning companies). This is why we moved to Braille.
My senior design project was for the blind, however we realized that the text to speech wasn't where we wanted to go because we felt Braille was better. With Braille you can multitask better, easily go back and pause and most blind people can read Braille a lot faster then they can listen.
