This number of bundles gives a nice and natural volume.
It is of course possible to vary in numbers. If you like a lot of volume, choose more Double Dreads. If you don't like a lot of volume in Synthetic Dreads, choose more Single Ended Dreads, this will ultimately create less volume.
You see Emilie in the video, who likes to wear a lot of volume, she usually uses 4 bundles of Double Dreads and 1 bundle of Single Dreads. So she also adds an extra bundle with Double Dreads. But Renate likes a little less volume, she uses 3 bundles with Single Dreads and 1 bundle with Double Dreads.
You can choose your own Dreadset completely to your preferences.