I enjoyed reading the CTX 3030 Handbook. I don't feel it was a necessity for me as I already had a very good understanding of the machine, but I still picked up a couple of things and feel those were well worth the $20 I paid for the book.
As for the Deus, I'm a complete noob with that machine and still have a long way to go before I'll feel confident using it. So I ordered a copy of Andy's Deus Handbook which I'm sure will be very helpful. The members here on the forum have already been extremely helpful.
For the $20 price, I say you can't go wrong even if you have a lot of experience with your machine. Even if you only pick up one or two useful tips, that alone is well worth the price IMHO.