Let’s start with the concepts: A direct drive wheel is a slimmed down design with a sprocket bolted straight to the hub. Nearly all off-road dedicated motorcycles come with a direct drive rear hub. A Cush drive is designed to reduce stress on drivetrain components during gear or throttle changes. It has a separate drive hub that interlocks with rubber dampers between those interlocking fingers. The sprocket is bolted to the outer drive hub or “Cush drive”. Those rubber dampers soak up energy that is produced when a shock load occurs from hard acceleration or braking. This is the common design used by almost all street motorcycles that effectively reduces wear and fatigue of the transmission and drivetrain.
Do you absolutely need Cush drive on a street/Supermoto conversion? No. It serves its main purpose for 600-1200cc asphalt-ridden bikes with much more power. However, a 500cc or less dirt bike can still benefit in the long run from a little less wear and tear on the drivetrain.
If you plan to race your Supermoto, lose some weight by sticking with direct drive hubs. The less rotating mass, the easier it is for your bike to accelerate. Cush drive also adds parasitic loss and when you’re dealing with relatively small displacement like a 250 or 450 dirt bike, you want to utilize every ounce of power, and drop every ounce of weight possible. 250cc 4-stroke machines benefit little from a Cush drive. It is not even an option on some bikes such as the CRF250L/300L and WR250R/X. On the other hand, a Cush drive can be very beneficial on larger displacement KTM’s, Husky’s, Yamaha’s, and Honda’s as well as Suzuki DRZ’s.
So, in summary, while it’s not a necessary “upgrade” it is a relatively inexpensive one when compared to the potential risk of added wear and tear on your transmission and drivetrain. If it’s an option for your model—and you’re using your Supermoto for street riding, not racing—it’s a decent choice to upgrade to.