It's pretty practical so far. Right now I'm just finishing up chapter 4 (HTTP Servers, Routing, and Middleware), so I haven't completed all of it. But as it stands, a lot of what you go through, you reasonably expect you may be able to use on an actual pen test. The real power though, is when you're building out your own tooling with these things.

You just set up a framework in the book, but this is all easily extendable to whatever you want. I'm not the best at Go, so it's a useful "nightly devotion" of time to spend working through it for an hour or so.

I've also been going through Writing an Interpreter in Go, and have picked up the companion to that Writing a Compiler in Go. So far, that's pretty good too, but I'm focusing on Black Hat Go first, to complete it.