A book about the mind will inevitably cover ideas you have seen elsewhere - don't think that because this book is written by someone on the autistic spectrum you will find it completely weird. And that's the point - Daniel Tammet comes across as interesting, facinated in the world around him and having a far better understanding of autism than the those who have built their careers on the subject.
A particularly illuminating moment for me came with a comment about a study into children with autistic-spectrum disorder, comparing their creativity with a control group. One question was "how would you make this toy more fun?" - the control group did better than the kids with ASD. But as Tammet explains, for someone who sees detail before they see broader issues (and as Tammet says of himself, someone who sees the scratches on the table before they see the table), this is such a sloppily-worded question that it's incredibly difficult to answer. What kind of fun? Fun for whom? When?
Understanding this, and taking savant skills out of the realm of the superhuman & into the real world, is one of the book's key strengths. The principal weakness is that Tammet isn't an incredibly engaging writer and can come across as a bit stiff and stilted at times - but this is in the nature of his brain, so it would be a bit foolish to expect otherwise and considered in this context he writes with great skill. The book challenges preconceptions about autism without being judgmental or confrontational, and has left me thinking quite a bit about the nature of the brain. Well worth the purchase.