For purely cosmetic reasons.... I bought some winglets and painted them the same off black as my 2016 ZX10R. Paint is from the company called "Tough Up" I think...
Someone made a thread on zx10 FB page and I saw a good deal of the UK guys who painted the winglets to match their custom painted bikes.
Performance wise... I see no difference at top end speeds.
Look wise, it's a take it or leave it..Im sort of neutral, but it makes my bike stand out when parked. It def get more looks now than before the winglets.
Theoretically they would generate downforce. And if so, then they should shorten braking distance by giving the front tyre more traction. But I would conjecture that the effect would be marginal and only really relevant when you need to stop from like 180 when there's plenty of drag to generate downforce.