The length determines the strip line on the ribbon itself.
Normal has a strip line of 2.5 cm.
This size adapts to those who have 'normal' eye shapes, ie small or normal eye shapes size.
Normal plus has a strip line of 2.8 cm.
This size is suitable for those who have larger eye shapes. This may be due, for example, if one's eyes are more open or longer in the eye shapes.
If you are the type who often cuts and adapts your artificial lashes to your eyes themselves? Or if you are in doubt about which one strips line / length you need to apply? Then I would recommend that you take the Normal version.