I thought I'd share my experiences with the 2 windshields I' have: the 19" off brand $45 one and the 4x the cost 24"+ VStream
The VStream I managed to position to my liking and it offers excellent protection and pretty much no buffeting for me at 6'4". It is installed on handlebars bars with 2" risers, so it is like a 26-27" tall screen on stock risers
. I can ride fully upright and not worry about wind. It needs the bottom secured, or it will rotate from wind pressure. With bottom secured it is good.
This week I removed the VStream (selling the bike) and without it the SR feels better (just like my Vectrix felt better with a smaller sport screen vs. the huge winter screen). Large screens just reduce the agility of the bike.
I think the VStream helps with mileage. Ride at 40-45mph without a screen and without ducking, and I think my mileage drops to the same as I'd get at 55mph with the VStream. Roughly.
I reinstalled the smaller cheap screen yesterday. This time I used different mounting points in the middle of the handlebars where the bars are thicker. Still wide part up. It now looks a lot like the Zero touring (larger) screen. I think this mounting is better and more stable. No buffeting on my helmet, air stream hits me in the face. Fine for city riding, but for faster than 45mph ducking behind is needed. For shorter folks it might work better.
I also "flattened" the fairly rounded shape of he wider portion of he cheap screen. Heated it up with a heat gun and pressed down to flatten and widen the wide part. Not fully flat, but it gained an inch or two of width and is less rounded. I think this works pretty well and is closer in shape in the wider/to section now to the MRI screen from Zero. For summer riding I prefer a smaller screen, so this works well.