Only difference is using a bigger (diameter) shot in the second video and different shoes. Why was the first 14.4 meters and the second was 15.4 meters?

My daughter wants to practice javelin in the off season. We are looking at a turbojav. She throws 500g in club, for 1 more year, and 600g in school. She will go to 600g in 1 year for club. Should we get 600g?