The phrase "a complicated one for" is correct and usable in written English.
It can be used when discussing a situation, task, or concept that is difficult or intricate for a particular person or group.
Example: "This problem is a complicated one for the new team members to solve without prior experience."
Alternatives: "a challenging one for" or "a difficult one for".
But Pessina and Walgreens management described PillPack as a small player and the pharmacy business as a complicated one for Amazon to take on.
Like other deployments, Inauguration Day will be a complicated one for the D.C. National Guard — at least on paper.
The race was a complicated one for the Republican candidate.
Which could make this winter a complicated one for the Redskins.
Analysts say el Chapo's latest capture gives the president a chance to regain some credibility, although the question of extradition remains a complicated one for the Mexican government.
The cause of Arab women is a complicated one for American partisans, after all, as it forces the left to give up (or at least to modify) its multiculturalism, and it forces the right to finally think seriously about feminism.
But newspaper industry analysts cautioned that the quest for Spanish-speaking readers is a complicated one, particularly for any media company that perceives the nation's nearly 40 million Hispanic Americans as monolithic.
I mean, I've seen all the movies, but the process of keeping a movie alive for 30, 40, 50, or more years is a complicated one, especially for one that pushed the technical boundaries of filmmaking at the time.
The task would have been a complicated one even for a stuntman.
But the point is that Posen is creating a story, and not a very complicated one for people to understand.
Mr. Mayor, you had a political decision to make, and it was a complicated one, whether to run for President, whether to run for governor in the same year, 2020, or maybe the Senate down the line, in 2022.
