Despite all the problems I detailed last post about Derleth's continuation, I'm glad the House fragment was published because we get some substantial information on the Conrad and Kirowan characters from it.
We learn that Conrad is a fan of a crazed poet named Justin Geoffrey, to the extent that he's investigating the man's family history and trying to find out just why he was able to write such darkly beautiful poems. It further drives home the impression that Conrad was a goth as a teenager. Not with the attitude that everyone hates him or the eternally depressed outlook some goth kids seem to have, but the sort of goth kid who only reads the work of writers who committed suicide and tries to break into the funeral parlor at 3 AM so he can see what a real dead body looks like. The really creepy kind of goth kid.
We learn that Conrad'll write to public officials in other towns requesting information about supernatural occurances, and that he knows how to phrase those questions so that those officials to answer him. He's a skilled researcher, and despite his really odd interests no one ever dismisses Conrad as a crank. Judging by the info he's gotten in The House he probably comes off as a journalist or a biographer when you meet him in person. His occupation might be somewhere along those lines.
We learn that its understood that Kirowan will accompany Conrad on any stupid venture he decides to undertake, at least as much because of his own interest as because of friendship with Conrad. One of the few lines Derleth cut from Howard's fragment was Conrad's statment about Kirowan: "I don't even bother to ask him to accompany me on my weird explorations any more -- I know he's as eager as I."
And we learn that Kirowan is five feet and ten inches tall. From there we can infer that O'Donnel and Vrolock are both at least a few inches shorter because Kirowan was described as tall in Haunter of the Ring. That really doesn't help with solving the mystery of who's narrating the other stories, but I'm a nerd and I can't help but notice little details that help me get the staging right in my head.