I have them in pdf too, but I'm definitely forking over the money to buy all of the CBTs (3-10) before I take the real thing. I think this is the best resource out there for practicing the new CBT, making sure there aren't any timing issues, and testing where you stand. Also, I really like how they give you a break-down on how you performed in specific topics like solutions or translational motion (when I see that I got 0/3 or 0/4 right for a topic it really sends a red flag), and you can click on those links to see all of those types of problems together, with the solutions (you can also choose to take the exams with the option of pressing the "solution" button to see the answer before you move onto the next question). They also show you on average how many seconds you take to answer VR vs. BS vs. PS. And I'm not paying for a course, so I guess I don't mind so much paying $35/test. And for those paying for Kaplan, I think they have access to the CBTs included.
My suggestion is to take 3R first and see what you think. If those aspects are worth it to you, it'll be clear and you'll be happy to pay the extra money for the CBT versions. If you don't think it really matters to you, then just stick with the pdfs. Good luck.