Just another opinion.
I had the Givi and it's great for keeping the wind off you, better than stock.
Was heading down to the Pyrenees September 2015 and thought I'd take the top part off as it would keep too much cool air from me. Big mistake!
The turbulence with just the bottom part was far worse than a stock screen. It's obviously designed as a complete item and it does that job really well. on it's own, not so good.
Remember, screens are a subjective thing. What's good for one person, may not be suitable for another.
For me, I went back to stock as I prefer to be able to see over the screen a bit more and found that when it rained, water was forced down the inside of the visor.
Like I say, it's subjective.