Messenger Blades are basically Enchanted Whetstones that require Exotic. Is there any reason whatsoever that these are even in the game?
They're different enough from each other. You can't attack with the whetstone, they're made of different materials, and the whetstone is less gp and thus more common.
The messenger blade has a bunch of things that make it more impractical to use in combat than a whetstone. -1 str, -2 con IIRC, as well as - enchantment bonuses.
It has a +1 enhancement bonus
I think the point here is that why would people want to find a more specific, bad version of a whetstone that takes the place of an item they 'could' have gotten. And I'm sure if you compared the value of this kukri to other kukri's in the loot tables, those are better too- So in a situation of combat where someone is going to use a kukri, this will just be another use-and-switch (like the whetstones.)
The whetstone is utterly useless as a weapon, even more useless than the messenger blade. You can actually
hit something with a messenger blade. And yes, there are better kukris. So what? There aren't a whole lot of kukris to choose from.
On the topic of -stat items sucking, they really do. I'd maybe use things that lower int/wis/cha, if I didn't need those stats for other things, but str/dex/con? C'mon. Nobody is realistically going to use those unless they're in a situation like Bruhm, who has 18 con and can afford to wear -2 con armor that gives him decent DR.
If it had negative int/wis/cha it wouldn't have
real drawback, because the characters that need those stats would never use a kukri anyway.
In any event, the messenger blade is sufficiently different from the whetstone that it does not qualify as a redundant item, and discussing stat penalties is off-topic for this thread.