There is not a huge difference between the First Aid books. However, they do update the First Aid books each year and there usually is a noticeable difference. A lot of the times they add new pictures or clarify certain concepts. I always recommend having the most updated book. However, if your current book is within one edition (2019) of the newest edition (2020), then it may not be worth buying a brand new book. But, it is probably worth going for the new edition if you currently have the 2018.
Hope that helps!
- Annette G, MD, MPH - USMLE Tutor and Residency Advisor at Med School Tutors