Just added the Givi 447FZ tail rack, with M5M monolock plate, to the bike. This will allow me to use the E26 box I had on before (and on my Ninja before that). I've had the Givi E21s with Givi side racks on since last year.
Givi makes a great product but they MUST have the worst printed directions ever. But I knew this going in. I had to undo most of the side racks to slide in the tail rack. Just kept everything loose till it was all lined up, then tightened the whole system down. I am very impressed with how well the 2 racks fit with each other.