I have actually used that for some things, although it's hard to know why the books there are there. Is this one guys opinion? sourced from uni courses? Consensus from some conference etc.

It's a little frustrating because I don't know much what I don't know but I also have limited time and I can't just study everything. I'm potentially struggling in certain aspects where there's some technique that makes it massively easier.

Certainly in everything I have learned more formally there's a huge amount you can get from one of the few gold standard texts. Like if you can do quantum optics by fox you're basically just ready to go work in a photonics research lab (at an entry level), even trying and finding out what you can't understand in that book will tell you exactly what you need to go study.