I've got the Kappa on my GS. I am 189 cm tall, and it works very well. With my height I get some buffeting on the helmet at around 100 km/h, but not much. If I bend down a little bit it is totally quiet, so I'm guessing that if you're less than 180 cm it should do well at highway speeds also. I've got the high seat on mine which puts me a bit higher on the bike as well. Speed limits in Norway is mostly 80 km/h, and at most 100, so it's not a real issue on my end.
I had one of these deflectors mounted on the original screen while waiting for the Kappa, but I haven't mounted it on the new screen as it had cracked the plastic on the old one. It is mounted with set screws that are covered with a rubber flap, and if you tighten these too much - the plastic might crack. Don't know what material the original screen is made of, but I wouldn't expect Lexan to crack like that. Maybe I'll put the deflector on and be careful not overtightening the screws...
2018 G310 GS