Absurdly Sharp Claws: …yes, of course someone applied mollyblade technology to a set of dar-bandal fighting claws. Notwithstanding that under most circumstances having claws that can slice happily through armor-plate is the very definition of Awesome But Impractical.
Awesome but Impractical
You Can’t Sheathe It, Either
“Excuse me? Could you tell me why this sword is so highly priced?”
“Ah, that’s because this is a mollyblade. The edge is single-layer graphene, less than a nanometer thick. It’ll slice cleanly through anything but muon metals, gluon string or neutronium – or antimatter, of course – and we can make-to-order one for you that’ll slice muon metals, too.” The shopkeeper carefully slashed the blade through the air. “See the glow around the tip, where the blade moves fastest? Dissociated air molecules recombining. It’s that sharp.”
“And that costs a million esteyn?”
“Well, not strictly speaking. The problem with the mollyblade is that a blade that sharp is also fragile. It damn near blunts itself on air molecules, too, which is a problem a lot of the lab applications don’t have. So what you pay most of that million for is the on-the-fly resharpening system that keeps it that way while you’re hacking and slashing with it.”
“Which is…?”
“Proprietary. Very proprietary.”
– overheard in an Eye-in-the-Flame retail outlet
Trope-a-Day: Awesome, but Impractical
Awesome, but Impractical: Given just how many tinkerers there are (see: Home Inventions) around the place, this happens a lot. Fortunately, the Imperial Military Resource Board and its commercial parallels are pretty good at filtering out the ones impractical enough to get people killed and battles lost before they hit production.
For modern examples – well, rather than repeat myself, go check out More Dakka and read the last couple of examples: the Dyson laser that can’t be aimed in any sort of reasonable timespan and the antimatter-grenade Gatling-gun. There is a reason why you will never see either of those on any canonical battlefield; this trope is it.