How common is the French loanword "métier"?

Our daughter lives in Leeds and is a scientist too, although not in my field, her speciality is haematology. My son lives in Manchester at the moment, for the music scene, he says. He writes his own songs. I think he's quite gifted of — course, I'm his mother — but he hasn't quite found his métier yet, perhaps.
_{Apple Tree Yard by Louise Doughty (2013)}

I think it is the first time I ever come across this French loanword, it's easy to understand—it's almost identical to the Italian mestiere—but I have never heard any English native speaker use this term aloud. Métier is very different from any of the alternatives I came up with which could fit in that excerpt: profession, vocation, trade, calling or forte. The last is yet again a French loanword but in my opinion it is far more common in speech and in writing than métier, although forte may be pronounced in three different ways, people understand it.

Because the protagonist of the story is a highly-educated, high-flying professional, does métier sound appropriate, intellectual, or pretentious? Is it a term which the majority of English native speakers are familiar with? My English companion claims it to be old fashioned, is he right? Finally, is métier interchangeable with profession and/or vocation?

According to Merriam-Webster's Eleventh Collegiate Dictionary (2003), métier has been in English usage since 1792, and has two senses:

1 : VOCATION, TRADE 2 : an area of activity in which one excels: FORTE

I remember being most struck by its use in James Branch Cabell, The Cream of the Jest (1917):

Through such airdrawn surmises, then, as I have just recoded did Felix Kenniston enter at last into that belief which is man's noblest heritage....

"Or I would put it, rather, that belief is man's métier," Kennaston once corrected me—"for the sufficient reason that man has nothing to do with certainties. He cannot ever get in direct touch with reality. Such is the immutable law, the true cream of the jest."

I tried running Google Books Ngram Viewer searches for métier and metier in American English and British English, and got a couple of lovely line graphs that are, unfortunately, completely worthless as a picture of U.S. and British English usage of the words over time—because so many of the matches that the graphs are built on come from French books.

That leaves us to make do with anecdotal or impressionistic responses to the poster's question about how frequent the word is in English—not a very satisfactory basis for a solid answer on that point, in my opinion. The Eleventh Collegiate Dictionary has a usage note that suggests that the value of métier/metier is that it has a particular connotation at least somewhat distinguishable from an array of fairly close synonyms:

WORK, EMPLOYMENT, OCCUPATION, CALLING, PURSUIT, MÉTIER, BUSINESS mean a specific sustained activity engaged in esp. in earning one's living. WORK may apply to any purposeful activity whether remunerative or not [example omitted]. EMPLOYMENT implies work for which one has been engaged and is being paid by an employer [example omitted]. OCCUPATION implies work in which one engages regularly esp. as a result of training [example omitted]. CALLING applies to an occupation that viewed as a vocation or profession [example omitted]. PURSUIT suggests a trade, profession, or avocation followed with zeal or steady interest [example omitted]. MÉTIER implies a calling or pursuit for which one believes oneself to be especially fitted {acting was my one and only métier}. BUSINESS suggests activity in commerce or the management of money and affairs [example omitted].

It seems to me that if you want to express the idea not merely of a trade or vocation or even calling (in a general sense), but of a calling or pursuit for which the person in question is (or considers him- or herself to be) especially fitted, métier is an excellent word to use. But if you are writing for an audience that is unlikely to have that word in their working vocabulary—and I'm not sure how you would gauge that probability—you might do better to use a more familiar term that has a slightly different sense and use other words to clarify your specific meaning.

Métier seems unexceptional (and unexceptionable) to me, but it is one of those loanwords that — not surprisingly — will probably be better understood by English speakers who have learned some French.

This suggests that British speakers will be more familiar with the term than American ones, given that French is taught in British schools to a greater extent than it is in American schools; a comparison of Ngrams for the occurrence of the term in British English and American English seems to bear this out.

I don't think the term is old-fashioned; rather, it occupies a somewhat higher register than its synonyms profession, vocation and occupation.