Anyone with a DDI subscription should definitely check this article out.
First, it has some intro fluff text about a knight of the post and his conjoined twin trying to avoid a Mercykiller on the streets of Sigil. The most important thing about this little vignette is that they actually call him a knight of the post! In fact, the intro fiction is full of cant. Used accurately, too.
Then, it gets into the history of the Mercykillers. And it's accurate, too! Ten paragraphs of history, including the Sons of Mercy / Sodkillers divide. The only change from original sources is the inclusion of references to the new cosmology. The Sons of Mercy see the mulitverse as inherently ordered, but criminals are led astray by influences such as the elemental primordials, who seek to undo creation. The Sodkillers see it as inherently disordered, requiring a constant beatdown of entropy like the gods handed out to the primordials. Good.
There's a slightly... political bent to it. I was surprised by a phrase or two suggesting that Sigil was better off for being rid of the squabbling, treacherous factions. But that's cool, too. Whatever opinion you want.
Next, they give a consolidated and focused summary of each of the factions: the Sodkillers, the Sons of Mercy, and the core Mercykillers still operating under that name.
Arwyl Swan's Son is a level 17 Elite Soldier, of course.
They even included the Mercykillers' Code, verbatim from the Factol's Handbook, as I can tell.
Someone named Cruel Seirrah, a tiefling, is described as the leader of the Sodkillers. And it stats a sample Mercykiller captain, with backstory, who belongs to an immortal race that I can't figure out, but which might be some kind of aasimar-esque race.
Then it describes the Prison, other Sigil landmarks associated with the Mercykillers. Then, it lists plot seeds, including the return of Nilesia. Then, some stats for Mercykiller adversaries. Then, a paragon path for the Sons of Mercy.
All in all, a very cool article. A good balance of fluff and crunch. A faithful Planescape conversion. Definitely worth reading. It gives me a lot of hope for the Manual of the Planes.
Author's name?