I've got the same top case -- the 33L Shad. However, I've since replaced the clear reflector below, with the red -- just haven't taken a pic yet -- looks much better.
I compared the Shad and Givi Monolock side by side before I ordered the Shad, and from a mount, latch, and build perspective, I felt the Shad had the advantage. Otherwise, I'd have bought the Givi -- they were in the same $$ ballpark.
I don't feel it *at all* back there. Admittedly, my FZ6R is 100lbs. heavier than my CBR250r was. My first thought was to use it occasionally, since it's so simple to remove. However, like you, I can no longer live without it. I keep rain gear, change of gloves, neck gaiters, ear plugs, you name it, in there. I can do small grocery shoppings, and local 'round town trips have suddenly become *much* more productive. Amazing...
Anyway, enjoy it. (You might want to consider that red reflector... it would go with your red/silver CBR, and looks *really* good).