This is definitely a great investment to get when you can afford to pay for it. If not, get the Dotcom Secrets and Expert Secrets book for a starter as those cover quite a few things that is inside Funnel Hacks as well, and it is at a much lower cost as well. You’ll definitely learn a lot from those books combined with what you learn in Wealthy Affiliate.
People not in your market — Learn how appealing and comprehensible your copy is to those who aren't familiar with your market or product. Do you give them enough context to want to know more? This will help cover the common problem where your site over-assumes base-level knowledge on behalf of your audience. This is important because there may be a lot of people on the edge of your market who'd become customers if they merely better understood why they should be.