This review is for all 5 books in the series, because while I think they're harmless one by one, taken as a whole, they support rape culture.
Let me say that there is no outright rape in these books, but they are all steeped in the trope of a beautiful virgin (in this case one in each book) who only needs a forceful man to awaken her sexual urges.
While I love the idea of the four wallflowers working together to secure husbands, and the descriptions of the gorgeous clothing, the characters themselves are fairly stereotypical--the shy girl, the brash American girl, the dreamer and the down-on-her-luck girl from the gentry. The men are equally two-dimensional--the rake, the industrialist, the stuffy lord and the irritating American.
All of the female characters, the four wallflowers and a secretary in the last book, are preyed on by the men, who reduce them to quivering masses of sexual desire by forcing kisses and gropes (and in one case, oral sex) on them. It's always because the women are so, so desirable that the men cannot withstand their urges.
It's been almost 200 years since <U>The Lustful Turk</U> was written, but apparently we're still believing this trope, glorifying it and in all too many cases, acting on it.
We need to stop.