I have heard of it. I can't remember whether it was the cost or the program itself that deterred me. It isn't the best for dyslexia, but since you believe that your son is struggling due to other root causes, maybe the way that this program is different might be targeted toward him.
Did you see that they have a winter special right now? And they mention monthly options. What I would be tempted to do is to set up a trial or a one-month membership, to see whether it has any results before committing to 9 months. It likely takes time...a consistent effort over a fairly long time....most any program like this isn't going to show a ton of results right away, but a 9mo commitment seems like a lot without a smaller trial to see some small improvement to know you're going in the right direction.
http://www.fastforwordhome.com/winter-reading-program
I *think* that Homeschool Buyers Co-op might have had Fast ForWord as one of their sales before, but I can't find it now. These are two other programs I've seen people use. But again, most of the reviews and such that I hear ARE for kids identified with dyslexia, so I don't know whether these target what you need. But maybe look to see whether these have any better reviews relevant to you, or free trials, or cheaper cost overall.
https://www.homeschoolbuyersco-op.or...?source=113480
https://www.homeschoolbuyersco-op.or...?source=113480
I have some book recommendations that work on memory, that might be cheaper than a computer program, but will have to come back later to post them if you're interested.