My sister a semi-professional photographer has used them. But you have to note that she only has done prints, using their professional service with the lustre finish too. So the cheapies (19c) ones she has never tried, nor the photobooks.
Sorry can't be much more help than that, but I would bet that their books are printed on entirely different equipment than the prints and probably aren't any better than say Shutterfly who has really put a lot of effort into that part of the market.
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