I have the Kappa RA308 and am very happpy with its functionality and construction quality.
I sized it up against the equivalent Givi and decided it was better in most aspects. I can fit a surprisable amount of stuff in it although it doesn't allow you to fit an A4 folder/holder in without bending it slightly. My 14" laptop just squeezes into the opening... once in it's fine. It is really a day bag or a light overnighter when little or no extra clothes are needed, i.e. toiletries bag, laptop, first aid kit, pair of underpants, condoms, bottle of booze and little more.
It has convenient zipper-up-able extra volumen, whereby you gain around 4 cm in extra height. Often I find I need to open this up to fit stuff in like the laptop... once it's all in I can often zip it up at least half way round if not all the way, compressing the contents and thus making the bag more stable.
I ended up cutting off the safety strap that is meant to be wrapped around the steering head... as it just got in the way and the fixation mechanism is plenty sturdy enough.
The weather proof cover is transparent on top for visualizing the see-through map pocket on top... this thing is somewhat bulky and takes up around half of one of the "smallish) side pockets. I live in sunny southern Spain so often leave it at home to gain the extra room.
One thing I'd love to see on these bags are retractable backpack style straps, as you can fit quite a bit of weight in them and carrying them with the short strap for a lengthy period of time can be uncomfortable... not to mention that strapping it to your back would leave you with both hands free.
All in all it sure comes in Handy and I no longer have the Bagster tank-cover hiding my RC30 paint job.
Would also like to see them made with waterproof zips and materials so you don't need a rain cover.
One downside to this bag: it has to be removed to fill the gas tank; I once left it on my pillion seat and drove off without fastening it. Noticed it was missing and went back to find it on the ground. Since then I've remembered to reattach it all the time.
More than that happening I'm more worried about leaving it on the bike after filling up and going into the service station building to pay... it doesn't lock on with a key or anything so anyone could nick off with it...
The moral of the story... keep an eye on it and your wits about you.
EDIT: The safety trap I cut off doubles as a shoulder strap but it is uncomfortable and digs into your shoulder and there is nowhere to roll the thing up and tuck it in... so I cut it off.