Hi Shaun,
The “Cisco ASA All-in-One Next Generation Firewall” book is great. It’s up-to-date and covers pretty much everything. The only thing it doesn’t cover I think is Firepower so you might want to look for another resource to learn that.
“The Complete Cisco VPN Configuration Guide” is quite old so I wouldn’t recommend it, especially if you have the “all-in-one” book. The “Cisco Firewalls (Cisco Press Networking Technology) by Alexandre M.S.P.” gets good reviews and it’s from 2011. It might be nice to read just to review everything again.
In the ASA platform, version 8.3 (released in ~2010) was a major upgrade. The entire NAT configuration has changed. Another big change was around 2013 when ASA 9.X was released. That’s something to keep in mind when you look at books, they should cover at least ASA 8.3 or later.
I can also highly recommend the books from Andrea Harris (http://www.networkstraining.com) Those are easy to read and to the point. Great if you want to learn a couple of things fast.
Rene