Booby, I agree TC electronics is a great company with products that lead the way..Helicon being one..
I also am confident that Roland's harmonizer is pretty good, although I have never tried the G70 personally, there have been good feedback from users..
I have used the early models that had Roland's harmonizer and thought they were decent[E-600 and DisCover 5]..

I am totally amazed by accomplishments of musicians that are visually impaired..

Several years ago I tutored a musician friend on the Roland G800..
I have tried to tutor people with 20/20 vision, and they could not grasp the dept of the G800..

My blind friend would record our sessions, making notes of default pages and clicks to the page they needed to edit, also making notes of edit buttons and knobs. He set up Braille marks on all the buttons and knobs[If I recall there was close to 90 different buttons and knobs..

To make a short story, he mastered the G800.
What he lost in sight he surpassed the normal in hearing...And did I add, he is the top three players I ever heard.

My point being ,if you are like my friend, I would not be surprised if you mastered either model...Go with the one, your ears tell you ....that it sounds the best...