The hand guards that come stock with the Duke 390 are flimsy and practically useless in a head on crash or a serious spill. They have no metal reinforcement and are as strong as a thin piece of injection molded plastic can be. It would be safe to say that the only purpose they serve is aesthetic and really can’t be relied on for safety of your hands or hand levers.
I ordered a pair of Acerbis X-Factor Handguards from Amazon and replaced the stock hand guards yesterday. Fitment was very easy and I did it myself in 15 mins.