I have the OEM top box, it's the same thing as Givi V47 but with a Kawasaki logo and with color-matched plates. The color matching is what made me get the original one, it looks great on the bike and it wasn't that much more expensive than. You also get the key insert that lets you open the box with your ignition key.
The OEM bracket is much nicer than Givi's somewhat generic-looking SR4114
. It looks like an extension of the passenger's rails
. The OEM base plate is Givi E251 (with a Kawasaki logo).
The quality of that box is great. We've finished a long trip around Europe 3 weeks ago, I had the OEM box and a friend had the V47. Mine once fell down from the bike (due to my mistake) and has a few tiny paint chips. That friend went down twice, once hard enough to bend the bracket (and the handlebars) and the box also survived with nothing but cosmetic damage.
The drawback is it's pretty heavy on its own, due to being made of thick, durable plastic. The allowed cargo weight is thus reduced but I'm pretty sure we both overloaded ours pretty badly for that trip. It made absolutely no difference to the bike, I just had to increase the preload a bit.
The box doesn't influence filtering in any way, I forget I have it in the city, that's a big plus compared to the panniers.