I owned a Diavel, and currently own an X Diavel S. In short they’re two completely different bikes. The X Diavel S has a tear drop style tank, improved front brake calipers, different wheels, it has launch control, it’s belt driven, and has no quick shifter like the Diavel. Although you can buy it for around 800$. The X Diavel is the more premium of the two, and it shows when they’re next to each other.