Think of them as Vibroweapons from Star Wars. Transonic Weapons are a type of weapon used by Adeptus Mechanicus Skitarii, most infamously Sicarian Ruststalkers. These weapons emit a low insistent buzz that makes stomachs turn. When they strike armour, these weapons will adjust their hostile sonic field to match its own resonant frequency, quickly slicing through it.
Transonic weapons are far better weapons than chainweapons. Not only are they easier to maintain and simpler to create (Requiring only a single blade rather than a link of teeth), but they also generate a higher rpm and doesn't require constant replacement of wear and tear. Additionally, unlike chainweapons, transonic weapons won't get snagged by gunk, clothing and blood in which most chainweapons are vulnerable from, that and the fact that it isn't useless if it runs out of fuel beside being an improvised club.
However it's likely that the cogboys aren't hoarding these weapons out of malice or because of their Blood Raven like tendencies. Rather its sheer ignorance or outright dismissal. Unlike chainblade wielding Astartes, the AdMech treats Skitarii and other basic troops little different from cannon fodder. This a common practice since their inception. Even their closest equivalent to Tactical and Assault Marines are treated the same way. So the AdMech would see no point in handing Transonic Weapon STCs over to other Imperial factions. While their more indispensable troops are given Power Weapons instead.
The Power Claw of the transonic family. This battle claw that can turn muscle, bone, and fat to jelly. Each of its talons can pierce through ceramite like paper and can even grab hold on a chainsword or power weapon with ease.
On tabletop, the Chordclaw can only be used for one attack each fight (and no longer fleshbane), but does 1d3 damage that becomes 1d3 mortal wounds on a 6+. It is generally much more effective than the Razor but cost more.
The little brother of the transonic weapons, the Transonic Razor is a small and concealable weapon used for assassinating high valued targets. Additionally, it can be used as an effective backup weapon. It is unwise for a Guardsmen to use this as an actual shaving razor. Loss of chins. Too many.
On tabletop, these weapons are the regular flavor of Skitarii CCW. Fishes for mortal wounds on a roll of a 6+, only Ryza rerolls wounds, so if you want to focus purely on a close combat AdMech army, then use Ryza.
The Power Sword of the Skitarii. The Transonic Blade is used as a primary CCW. Its longer reach means that it is able to parry CCW of other races and factions effortlessly, in some case it could even slice a chainweapon in two due to its higher quality and rpm.
On tabletop, they are Razors with +1Str. Wounds marines easier, and can be combined with Machine Might to ravage guardsmen, but remember mortal wounds don't care about the target's toughness so if you roll a 6, you can say goodbye to that targeted unit.