Robert Heinlein really made his name during the 1960s and ̕70s, so these short stories are examples of his early work. There are two from the ̕50s and four from the ̕40s.
    The title story: a husband-and-wife team running their own detective agency are baffled when a man walks into their office one day and hires them to do a job the like of which they’ve never done before: he wants them to tail him. He leaves the house on time every morning and returns home each evening, but has no recollection of anything in between; one ominous detail, though, is a mystery deposit (red, sticky) under his fingernails. So he wants them to follow him and discover what he gets up to all day.
    “The Man Who Traveled in Elephants”: in this one a bus passenger, involved in an accident, bashes his head on the seat in front—and everything that happens next seems…different, too perfect…
    “All You Zombies”: an extraordinary time-travel story, eventually filmed as Predestination (2014).
    “They”: the story of a man’s unbending conviction—while under close observation in a psychiatric hospital—that the entire world and everyone in it is a sham and elaborate conspiracy against him (half a century before The Truman Show too!).
    “Our Fair City”: more whimsical fantasy than science fiction this one, as a newspaper reporter battles corrupt local officials—with a sentient whirlwind to help him.
    “And He Built a Crooked House”: an architect designs and builds a four-dimensional house—having four spatial dimensions that is, an object mathematicians call a tesseract or hypercube. So, from the outside, this house looks like a simple one-room box, surrounded by lawns and rose-beds; inside though there are no less than seven further rooms, all cubes precisely the same size as the first. The thing is this: getting in is straightforward, just through the front door, but can you find your way back out again—ever?
    There was only one story here I didn’t think much of and, overall, this was an enjoyable and interesting read. ( )

Although it has a mediocre plot, The Unpleasant Profession of Jonathan Hoag has solid mechanics. Robert Heinlein wrote a great short novel or long short story with this one. He generally wrote hard science fiction, but this is more of a horror/suspense piece.. The other stories in the collection augment the overall value of this volume. ( )

Some stories were good; some were bad. I liked "They". ( )

The stories in this collection are interesting. What is difficult is to read them now in the 21st C for the first time and to try and bracket out the stories published since this mid-20th C book that were influenced by it. As a result, I was able to predict the plot outcome early in the story simply because many stories since have emulated them. The first story is the namesake of the book is interesting and one of the stories that has not yet (to my knowledge) been yet thoroughly borrowed by subsequent writers. So although I suspected something like the conclusion, I was still a little surprised. All You Zombies is a fun time travel paradox but I think Heinlein did it better in his The Door Into Summer. He Built A Crooked House was also fun but it is clearly reflected in The Matrix movies by the Wachowskis (especially Reloaded) and also Inception with their play of the (meta) physics of houses and cities. There are three other stories in addition to these: The Man Who Traveled in Elephants, They, & Our Fair City. What binds all of the stories together in my mind is how central characters are not cognizant of the fact that they are not in possession of all of the facts and are to some extent pawns in a game they don’t know they are part of. This is early Heinlein, so I enjoyed it. But it is not his best. For short stories, his best are found in the collection The Past Through Tomorrow. That volume contains some of the best Sci Fi short stories I have read.

I like this rating system by ashleytylerjohn of LibraryThing (https://www.librarything.com/profile/ashleytylerjohn) that I have also adopted:
(Note: 5 stars = rare and amazing, 4 = quite good book, 3 = a decent read, 2 = disappointing, 1 = awful, just awful.) ( )

Robert Heinlein is one of the finest science fiction writer of the twentieth century. 6 x H is a collection of a novella, "The unpleasant profession of Jonathan Hoag," and five short stories. Hoag is a gentleman who goes to work but has no memory of what happens during the day. When he finds a strange substance under his nails, he asks two detectives to help him sort it all out. Teddy and Cynthia find themselves getting into more than they bargained for.

The other five stories are vintage Heinlein. A travelling salesman gets to attend a fair; an unmarried mother asks questions; a man struggles in an insane asylum; a whirlwind named Kitten keeps trash she finds; and, the best story in the book, an architect builds a house in four dimensions.

This is vintage Heinlein, unlike many of his later works which are different from the early years. ( )