I thought the same until they arrived. They aren't just small extenders, they are a (almost) full sized guard that sits behind the OE guard, and extends above it.
It's a bit of over engineering, but it's good in that you can remove them later if you choose, without leaving any screw holes.
They do make a difference in the wet, though I've got some rather special Halvarssonns gloves and I can't tell if the the gloves of the guard extenders that are keeping my hands warm in the English winter. Or maybe both !
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I also have a Kiess Heated body warmer, it just warms the Kidney area and worked brilliantly for me in northern Scandinavia a few years ago, that and heated grips.