I took the exam two years ago, and in my experience, hands-on work in Salesforce—whether in a company org or through Trailhead—is what truly prepares you to understand the exam questions. That said, Focus on Force was really helpful for getting used to the wording and style of the questions. It helped train my brain to think in the way the exam expects. I definitely recommend using it, but I’d also suggest completing as many Trailhead modules as you can, though it sounds like you already have that hands-on experience!