My problem with the OE guards is that their position is fixed in relation to the levers, because they anchor to the lever perch. So if - as I prefer - the levers are tilted slightly downwards, then the guards are also tilted down, and leave much of back of hand exposed to the weather. The BB Storms anchor to the handlebar independently of the lever perches, and (I hope) can be positioned to provide maximum coverage of hands. So although the actual size of the Storms is not greatly different to OE, the weather protection provided may be.
Highwayman2016 - thank you for taking the trouble to shoot and post photos of the installation on your DL650: much appreciated. That looks promising, although of course the V2 has a hydraulic clutch, so space for mountings on the clutch side is more limited.
In the winter, I fit Tucano Urbano muffs, which are great, but in the summer prefer not to have them fitted. However I live in Wales, where rain in summer is not entirely unknown! The handguards on my old R1100GS, although not much bigger than those on the Strom, kept my delicate pinkies in summer gloves completely dry; that's what I'm hoping to achieve.