The edition I read, a trilogy of the first three Alleyn mysteries and an early short story, was published for Alleyn's Diamond Jubilee, and contains a fascinating introduction by Marsh detailing the birth of Roderick Alleyn. The Christie/Sayers connection is very important, they are clearly huge influences on her first novel. There is a little of Lord Peter Wimsey in Alleyn, and a lot of Agatha Christie in the country house murder and death by a dagger with exotic connections. There's also a touch of Saxe Rohmer and other adventure stories of the day with a troupe of Russian anarchists who have to be arrested before the murderer can be revealed.
The Russian anarchists I found tedious, the murder was clever, although the unmasking of the murderer was not terribly convincing, but, not bad for a first effort, and as Marsh was to prove, Alleyn was to become a great stalwart of detective fiction, with some truly brilliant novels from his creator. It's a fun read, not terrifically believable, but great to read on a lazy day.