I have System 3 cases on my moto. They're slightly wider and the covers have a rounded contour. They've been launched across pothole fields and tumbled down rip-rapped river banks. They've been beaten on and one had an organ replacement but they haven't been defeated, and they can be repaired in the workshop.
They are excellent as crash guards. They make lifting a dropped moto easier. Your System 2 cases will likely lead a more sedate life than mine.
The fault of these cases is the latch that secures them to the z-rack. Its grip can become loose enough that it can flex open sufficiently to release the case if the moto powers over a deep pothole or a pothole field. Adding some rubber sheet to the forward inside plane of the case where it contacts the z-rack will tighten the latch's grip on the rack. Put your contact information in an inconspicuous place on the case so it might be returned to you after you blissfully bounce away from it with a hearty Yeeeeeehaw.
I'll definitely put my contact info on the cases so if they are ever lost on a ride....
The cases "seem" to be really tight on the Z-rack already. Going to put them on again today and will evaluate the need for the rubber sheeting as you suggest. No tumbling down river banks for me on the K75. Too old. Too smart. Well, too old at least. The rough housing is Vespa territory. I've slid it down slag heaps, across rough stuff my Adventure bike friends don't attempt, and if I only had knobby tires I would be exploring the single tracks here. But the K75. It lives on pavement. And the occasional well-maintained gravel forest road.
Thanks for the suggestions on the side cases.
BTW -- I was called out yesterday for calling them side cases. Was informed a real BMW rider would refer to them as Krausers. Am I real or a pretender??