The Givi Airflow works very well. What I don't like so much about it is:
- It vibrates pretty strongly when extended more than 50% and at idle.
- The plastics are not as good / scratch resistant as the BMW OEMs.
- My wife didn't like it. She got more buffeting than with the GSA shield in pretty much every setting.
- It doesn't look really bad, but it also doesn't look really good.
The first two items got me thinking about selling it, especially as I have a GSA windshield which works pretty well for me. I can put the Touratech spoiler on whenever I need to do long runs and still have a setting that works well for me when it's not on.
Windshields are a very personal thing. It depends on your sitting height, your seat, your helmet, the helmet fit (tighter fit == less buffeting), your earplugs, your jacket, your handguards, the angle, your personal hearing, and so on.
You plain can't buy a windshield just because other people like it.
Everybody I heard of loved the Aeroflow for the F800GS. For me, it was giving me a really, really bad headache when I was above 60mph for more than 30 minutes. Discomfort started with 15 minutes above 50mph. That doesn't mean the Aeroflow is bad windshield - it means it didn't work for me
I have no experience with the VStream, though I am interested in trying one some day.