The strut design is very different and actually creates a complete X all they way back to the battery chamber. The struts between the motor mounts and ducts are fragile and break easily. So these upgraded frames stiffen the struts considerably. The struts themselves have a flat cross section which creates more bonding area with the duct.
Here is the review by krachall at RCGroups.
RECOMMEND PARTS LIST
- Frame: Beta75S frame (just this one)
- Motors:Â 8x20mm 14000KV motors
- Frames: 40mm 3-blades props / 40mm 4-blades props
PACKAGE
    This plastic durable package can protect the package from deformation duringÂ
   the shipping process. (Shipping weight is cubic)
- 1 * 75mm Whoop clear plastic frame (Fit 8x20 motors) Beta 75S
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