The phrase "applies mostly to" is correct and usable in written English.
It can be used when indicating that a particular statement or rule is relevant in a majority of cases or situations.
Example: "This guideline applies mostly to new employees who are unfamiliar with the company's policies."
Alternatives: "is primarily relevant to" or "is mainly applicable to".
Among my adult friends, your column applies mostly to Friendster.
This applies mostly to those who take them on a daily basis rather than only occasionally.
We still don't have the level of detail or knowledge to answer that," says Bowman, although this applies mostly to non-medical products.
The designation applies mostly to a small segment of the line, between Union Square and the Lorimer Street station in Brooklyn, but the highest concentration of hipness is achieved between just two stops, Bedford and the First Avenue station in the East Village.
This issue applies mostly to the purely prediction-driven transformations that do not have sufficient experimental evidence to confirm the predicted effect (so-called "amplified" transformations).
This urgent view applies mostly to companies that depend on technology for their very livelihoods–say, a social networking site like News Corp.'s MySpace, a blog (like my own) or a company hawking an entirely new technology, such as a voice-over-Internet Protocol carrier.
After college, DeBaise applied mostly to tech startups.
Until recently, electronic monitoring applied mostly to Web browsing.
Dr. Solomon said the alert was likely to apply mostly to specialty products sold in Asian markets.
The much-misused term "auteur" was applied mostly to film directors working as contractors for the Hollywood studios who, nevertheless, revealed their own distinctive style and personal vision.
The increases take effect Aug. 17 and apply mostly to Asian goods that travel by a combination of rail and truck from the West Coast.
