Well, the main reason is Monty Egg himself. Though we get to know very little about him over the course of the stories, we do get a strong impression of who he is. He is essentially a flat character, but enjoyable company nonetheless. He’s observant, polite and helpful at all times, and is religiously devoted to his work selling wines and spirits – his sacred text being the Salesman’s Handbook. In every story, Monty will find a way to apply the rhyming aphorisms from the Handbook to the problem at hand, and there’s pleasure in seeing how this predictable pattern will be fulfilled in an unexpected way.

It’s also really interesting to learn about everyday life in the 1930s. Monty’s profession, the “commercial traveller”, is not something that really exists these days. Sayers always makes sure Monty is “on the spot” for a job-related reason, and things like his travelling schedule and interactions with other commercial travellers are often important. New developments such as artificial scents and petrol station chains are featured, as are the quirks of train tickets, grandfather clocks, and chemists.

In all, these stories are a fine entertaining time. Monty would hate it if you binge-drank one of his wines, and bingeing his short stories is equally inadvisable. I think the similarities would get to you after a while. Perhaps the best way is just to have the occasional visit from Monty once in a while.

If you read only one story…

…read Maher-shalal-hashbaz. Ok, so the story is an unusual one compared to the rest, but that’s it’s strong point when considered on its own. The central scheme is so out there and horrifying that it stands out.
If you’re a cat lover, maybe go for the abundantly-clued The Professor’s Manuscript instead.

The Poisoned Dow ’08

Montague Egg arrives at the home of a client to discover he’s been poisoned by the port Monty sold him on the last visit. Unless the poison was in the port when Monty sold it to him, the murder must be impossible, so Monty has to get himself out of a pickle by finding the real killer.
This serves as a great introduction to Monty Egg. It’s one of the few stories where it’s actually Monty’s knowledge of wine that helps him solve it. Though even a wine-savvy reader (which I’m not) could not “solve” this one, as the clues are only revealed when Monty explains them. Since the story is almost entirely a discussion between Monty and the police inspector, it feels a bit static. The murder method is ingenious, though.

Sleuths on the Scent

Monty finds himself at the first of many underwhelming pubs just as a radio broadcast calls for a murder suspect to come forward.
This one is a bit more fun, giving the readers multiple suspicious characters to pick from. The clue the story turns on is pretty weak, but does provide some good 1930s colour. Sayers’ “group discussion” scenes are an under-appreciated part of her talents, and I enjoyed this one very much. Monty’s method for catching the suspect is groan-worthy, though.

Murder in the Morning

Monty Egg goes out of his way to talk to a prospective client, only to find the man lying dead. The obvious suspect is the man’s nephew, but then new evidence proves that he can’t have done it – and the only other possibility is Monty.
“If you’re a salesman worth the name at all, you can sell razors to a billiard-ball.” …if you say so, Monty.
That eccentric aphorism sets the tone for what ends up as a farcical story, featuring a man with the numberplate WOE 1313 and a witness named Millicent Adela Queek. Going for maximum silliness is probably the only way to get away with the solution to the alibi, which is totally ridiculous. For modern readers this story does provide some extra “period” interest in the details of petrol stations and car usage at the time.

One Too Many

After a financier vanishes (along with the company assets) from the train Monty was travelling on, what Monty witnessed proves crucial in discovering what happened.
The opening sets out the problem neatly but does “threaten to involve a series of dry railway timetables” (as Death in Early Spring would have it). We follow Chief Inspector Peacock’s efforts to crack the case, then the rest of the story is Monty in conversation with Peacock. It is fun to witness Monty’s observations of the passengers, as his third-class carriage seems to have been full of people who could be the disguised financier. The Inspector’s gradual transition to trusting Monty to explain the scheme is also enjoyable, and the scheme itself is a crafty one. The ending has a neat punchline to cap off the story.

Murder at Pentecost

A chance encounter at lunch leads Monty to solve the murder of the master of an Oxford University college.
Monty’s good nature and curiosity net him a new friend who draws him into the situation (even if the new friend comes across as a bit of a jerk…). I also liked him inventing a new aphorism to help him remember an obscure point of politeness! However complication gets piled on complication, leading to the alibi creation in this story being confusing despite the basic idea being simple. It’s impossible to keep track of all the various passages on the campus. The story also feels unusually padded compared to the rest in this collection.

Maher-Shalal-Hashbaz

Monty’s good deeds extend to rescuing a girl’s cat from a tree and using his sales skills to help her sell it, before a Sherlockian scheme reveals a dark twist.
This story is very engaging and effective, from Monty’s unlikely heroics at the beginning, through the advertisement scheme reminiscent of one of the best stories in the Holmes canon (The Red Headed League) and on to its horrific conclusion. It’s much closer to a horror story than a detective story; of course, Sayers herself believed the two genres were closely related. The eventual conclusion is not one I’ll forget easily.

A Shot at Goal

The owner of a local factory is murdered after receiving a threat seemingly connected to the local football team. Monty will have to put the information he’s gathered about local tensions – as well as his knowledge of spelling – to good use.
The central clue in this is pretty dubious – the letter it’s based on is reproduced with an image, of course, but this doesn’t actually add anything extra to the story. It’s like it was reproduced simply because that’s What You Do With Letters in Detective Stories. Other than that, Monty is on good form, chatting to the locals and snooping around at the crime scene.

Dirt Cheap

One of Monty’s fellow commercial travellers is killed, and Monty provides the key evidence as to time of death – or does he?
The story stands out in its setting and characters being more grimy than usual for Sayers, and for Monty actually losing his cool for a bit. Aside from the good descriptions of the run-down pub, there’s not much here, as the solution comes out of nowhere once again.

Bitter Almonds

It appears a wealthy man has been poisoned via the medium of one of Monty’s products. There’s an obvious suspect, but fortunately Monty remembers some important technical details that might throw new light on the death.
An interesting and surprising story with an unusual solution. In a way, the main problem is not the poisoning, but in untangling the actions of other characters. The poisoning isn’t possible to solve without technical knowledge, but understanding the sequence of events is.

False Weight

Monty noses his way onto a crime scene again – this time, by identifying the victim. Monty’s fellow commercial traveler is in the frame as the killer, but the pendulum might soon swing the other way.
Another instance of the clue very specific to its time. I found it difficult to understand, even after the explanation. Monty’s transition to telling the police inspector what to investigate is a lot more unnatural here than in One Too Many, but I like how he manages the situation by making sure the right questions are asked to the right people (even though that’s a bit tragic here if you think about how it works out…).

The Professor’s Manuscript

Monty gets a tip off about a new client, but something seems off, so he calls in another client in to investigate and uncovers a sneaky criminal.
Clearly Sayers saved all the clues for the last story, as they turn up in abundance here – and they’re pretty good ones too. The narration lets us know that Monty’s smelled a rat even before he visits the titular professor. I didn’t catch what was wrong until the re-read, of course. A good closer to the collection. With this, the collection reaches an angular eleven stories – as Tony Medawar has pointed out, Eggs generally come in dozens, so why not one more? I wonder if Sayers just ran out of plots for Egg to get involved in. Even within its short run, there are a few repeated scenarios. And the number of murders that happen to Egg’s clients or to fellow salesman or to people Egg met in a pub is already pretty alarming.

Other opinions:

crossexaminingcrime
The Invisible Event