
This is my detailed review of the Givi windshield. I put one on the SRB several months ago, after reading several favorable reviews of it on this forum.
Spoiler alert: if you want to skip the rest of this review, here's the nutgraf: The Givi is very attractively priced. By all other measures, I consider it to be very mediocre.
First, an observation. The Givi definitely reduces the force of the air hitting the rider. However, the air behind the windshield which the rider sits in is very turbulent. For most of us, this may not be a problem.

But for me, I ride wearing T shirts a lot, and the turbulent air literally rolls up the sleeves. Which makes me look like some kind of 1960s James Dean wannabe poser.

The other thing, is that when I wear a helmet, it is a Biltwell or Fulmer open face style with a snap-on face shield.

Note that the holes for the snaps on the face shield are slotted so that it can accommodate different brands and sizes of helmets. What this means, is that the face shield is somewhat loose -- It jiggles. When sitting in that turbulent air while riding, the face shield jiggles and rattles noisily and constantly, loudly enough to drive you crazy. This was never an issue before the Givi.
My solution was to cram weather stripping (grey in the pictures) between the helmet and the face shield, immobilizing it. Doesn't look too bad, and completely solved the problem.
Now the review:
Price: 9 out of 10. Very affordable.
Effectiveness: 5 out of 10. Admittedly, it's a pretty small windshield so you can't expect too much out of it.
Looks: 4 out of 10. Honestly, you may disagree, but it's not very attractive IMHO. It suits the Super RustBucket just fine, but if I had a "nice" bike I'd be looking for something else.
Attachment system: 4 out of 10. I find handlebar-attaching windshields to be fussy-to-mount and janky-looking.
Attachment security: 4 out of 10. As has been noted by others, the Givi vibrates notably at idle. In my case, it is only the right side attachment that vibrates. Vibrations --> plastic fatigue --> eventual cracking.

I have a classic Harley style windshield on my Sportster. I wish they made something like this for the XS650. It is big. So big that it has vertical and horizontal chrome reinforcement strips across the Plexiglas. It blocks highway air so effectively that you could prepare English tea behind it while riding. It looks good, like a windshield is supposed to look.
It is rock solid, attaching at 4 points directly to the fork tubes.

Which means that you would have to get rid of the stock headlight brackets, and replace them with something like the above fork ears.
I know there are windshield threads, but I'd be interested to hear from others with windshields that they like.