Why not just mount the original BMW top case rack? If you’re lucky, you’ll find enough mounting points for the Givi rack. If not, you can attach an alloy plate to it and then mount the Givi plate. That’s what I did for the Shad 59X top box, and it’s absolutely secure.
I ordered the Roadstyler handle, backrest, and luggage rack. But for a fully loaded holiday trip with the 59-liter top box, I trust the original top case rack more. Of course, you can’t remove it as easily as the Roadstyler rack and replace it with the smaller handle or backrest, but it’s 100% secure. The weight is better balanced and sits a bit lower than with the Roadstyler rack.
Since I only use the top box for vacations, I swap the Roadstyler passenger backrest and luggage rack for the BMW top case rack. I get that some people might question the effort, but it’s just four screws (five, if i include the one for the seat) and three zip ties—and it’s a great chance to clean the rear wheel and fender.
If I were looking for a permanent top box setup, I’d definitely go with the original rack.
Just my two cents.
Best regards
Stefan