I think the knowledge of it carried over from my 1e OA days. Basically the same as the Kusarigama but it's got a dagger/hook at the end instead of a kama.
Mechanically speaking:
A whip-dagger does 1d6, has reach, disarm and trip.
A Kusarigama does 1d6, has reach, disarm and trip. (it may also be a double weapon.)
A Spiked Chain does 2d4, has reach, disarm and trip.
All 3 are exotic weapons that can attack adjacent opponents, can trip and grant a +2 on disarm and allow the use of Weapon Finesse.
Whip-dagger is one-handed and has reach up to 15 ft, and can't be used as a double weapon.
Spiked chain is two-handed has reach up to 10 ft., and can't be used as a double weapon (the latter being a surprise to me).
Kusarigama is two-handed has reach up to 10 ft., or can be used as a double weapon.
The kusarigama (lit. chain-sickle) is additionally described as being a kama on a chain.
Guess it's somewhere in between.
It's either a two-handed whip-dagger with reduced reach.
Or a slashing spiked chain with reduced damage.
It's inferior to both aside of its use as a double weapon, so if you want an alternative for the whip-dagger you're better off with the spiked chain, which is also less troublesome if you're not the DM, since it's in the PHB.
For the character I was designing when I joined this thread, I just gave him two weapons, a whip to drive his slaves and a sword to bash his foes. I think the fact a whip deals non-lethal damage might actually be the reason why it's a successful slave-driving weapon. You don't really want to kill your slaves, do you? And they are usually unarmored anyway, just have to make sure your slaves don't have natural armor of +3 or higher.
