You're a writer. You need reliable contacts either for screenplays, novels, etc.
Herman has an excellent and professional approach to providing a listing, with useful information which goes well beyond most internet listings or other sources.
Unfortunately, he felt it necessary to provide all sorts of agent-centric viewpoints (mostly his own) about the business, which are not really useful at best, and at worst irritating.
Looking at listings, you'll just have to ignore the "worst client" categories he proposed to agents... where agents had the opportunity to reply with things like "sends packages impossible to open..." (what an incredibly difficult life agents have, with such a clientele...). This is really worthless stuff, designed to belittle people and make them feel like supplicants. Which is ass-backwards. Agents should be grateful that writers ask them for help. Agents should see themselves as FULL partners (and lucky to be so...) in a project.
Don't be put off with, or buy into, the crybaby agent-centric stuff Herman throws out about how agents receive 90 percent garbage... that they have to "wade through" it. At least... don't buy how boring and painful that is. Because: That's. Their. Job.
Writers, Herman needs to be reminded, have a tough job, too. At the very least. They spend months and even years developing an idea... character development, style, point of view, a general knowledge of humanity/the universe/etc... and agents take about 15 minutes to decide if they like it or not.
Herman seems to think all that effort at creation, doesn't really count in terms of "work". That the work only truly begins, when the agent starts peddling the property. Or, worse, that only agents know what real writing is all about.
Don't be fooled. These people aren't "experts". They work the way a reader works in a bookstore: pick up... like/dislike. Put back or buy. But in their case, they decide on pick up or buy based on their personal contacts in publishing companies. They base their decisions on WHO THEY KNOW, and the tastes of THOSE PEOPLE. In general, they don't know squat about the real intricacies of writing, except that -- to be fair -- they can recognize when something is acceptable or not (although not always, if you look at quite a bit of the stuff that gets published).
So... don't base your personal sense of self-worth... or model your writing approach... on that attitude. Write what you need to write, with all the conviction you have, and if it works, it works.
If it doesn't... it doesn't.
But ignore all this agent whining about how tough it is to winnow through the thousands of manuscripts they get. Poor them.
THIS book, is indeed useful because when Herman has gotten away from his ego essays (some of which are outright incomprehensible, especially when he launches into attempts at humor), he does provide a useful list.
Good luck. But don't be cowed by this agent-looking-down approach.
You're the writer. YOU'RE the one these people are making money on the backs of.
Don't forget it.