"Absolute freeBSD" is good choice.
but did you read "Absolute OpenBSD " from the same author? I find is more interesting than "Absolute FreeBSD".
I red "Absolute OpenBSD" a few years ago. Before becoming a FreeBSD user. I agree with you that the OpenBSD book is better than the FreeBSD one. One the other side, OpenBSD is considerably slimmer than FreeBSD so making a book out of it is simpler and the book will be more compact.
These things, AFAIRemember, make OpenBSD "easier" to deploy just after install.
-] OpenBSD comes with only one firewall : pf (FreeeBSD has 3)
-] It has by default a nice shell : ksh (FreeBSD comes with csh, wich probably you will not love
and you will want to change it for your default user)
-] it comes by default with an editor for Emacs people which is "mg" (in FBS you need pkg)
-] it comes by default wih Perl installed (FBS, use pkg)
-] it has dhcp server by default. (FBS, use pkg)
-] It does not have the Linux compatiblity layer (in FBS has it and that opens new (wild) world)
-] ... it should have by default a web server, but i never used it.
==> These make OpenBSD ready to deply just after the install *if* you
want to do build a classic network service : NAT, dhcpd, firewall, VPN, Web ....
In FreeBSD you need to do some tweaking to adapt the system to your preferences, so making a book on it becomes more complex.
I have a list of things to perform just after I install each FreeBSD instance.
[0] configure network
[-] install mg, [-] install Emacs, [-] install bash, [-] install ruby [-] install pry.
=> Then I fix the configuration files and start to adapt the machine to what it needs to do.
bye