I just recently took the exam. Per training, a new version is coming soon. You might want to reach out to fortnet cert/training group and possible wait. I' m going to take it after it comes out and I see the objectives. I hope fortinet puts up a practice exam on their campus weblink.
As far as the book course, I can' t speak about it. But any training would beneficial imho.
I took the exam approx 1.5 yrs asgo, thinking it was simple, but it was not & I had approx 1-2 years of off and on experience with the mail security appliance ( scored a miserable 45% irrc ).
fwiw: I went back after another solid 1+ year of more experience, and passed just barely.
I had a few areas of scored at 100% and a lot scored <10% or 0% ( primary HA and transparent mode of operations ). So I think a combination of written, reading, hands-on experience is what you need. The 3 100% areas that I scored on, help dramatically.
All of inside fortinet contacts , also told me the exam is harder than the firewall appliances. It was probably as hard as the Cisco IronPort stuff.
That' s all that I an offer and advice that I can give.