There are at least three schools of thought on the subject of windscreens for a naked bike such as the 390 Duke:
---the "Naked bike purists" who seek a minimalist look and abhor any screen bigger than the miniscule OEM piece;
---Those in the middle, who look for a modicum of protection but want a sllek, racy look;
---Those whose priority is protection, who are unconcerned about looks and seek some real shielding from windblast.
I belong to the last group. At my advanced age I would like some mitigation of the raw windblast on my torso at 50-80 mph speeds. Did the naked thing long ago.
After considerable reflection, I decided to go with the MRA VarioScreen, a German-made, rather pricey, but superbly-designed product.
MRA VarioScreen (style "VNB") universal windshield for naked sport bikes, cruisers, enduro, and dual sport motorcycles - TwistedThrottle.com
This modestly-sized windscreen has excellent optics and is made of top-quality materials. A very solid design and a piece I expect to last many years. Many windscreens can push aside air and give you some relief, but invariably an unvented windscreen will form a pocket of low pressure behind it at speed. This low pressure area will cause the airflow to wrap around the screen to fill the partial vacuum, creating vortexes that the rider will perceive as turbulence.
Snapping, popping, buffeting, roaring, intermittently noisy, busy and frenetic. This typical behind-screen turbulence can be as fatiguing as the actual windblast itself.
This is the reason I selected the VarioScreen. A clever, two-piece design, the Vario's distinguishing feature is a large air intake at mid-height that provides two functions: The intaken air eliminates the low pressure area behind the screen, so no vortexes form; The intake directs a smooth, turbulence-free stream of air up towards the rider's face, enhancing helmet ventilation and reducing wind noise. This ingenious design provides excellent windblast protection, while at the same time eliminating almost all turbulence. Windscreen nirvana. It makes for a very relaxing ride at speed. I cannot recommend this high-quality piece enough. It is superb. Not sexy looking, not "naked bike pure", but brilliantly effective.
Attached photos show the VarioScreen on my "Dukino".