The phrase "a boon that has" is correct and usable in written English.
It can be used when discussing a benefit or advantage that has been provided or received in a particular context.
Example: "The new policy is a boon that has significantly improved employee morale and productivity."
Alternatives: "a benefit that has" or "an advantage that has".
Stricklin said talent was more evenly spread in the conference partly because of the boon that had come from revenue-sharing.
It's a boon that we have laws and social parameters that keep racists, sexists and homophobes in check.
He is also a boon for an airline that has filed for bankruptcy twice in recent years and has been plagued by publicity nightmares.
That would be a boon to an industry that has experienced sharp declines in sales since Donald Trump's won the White House in 2016, after years of record sales driven by fears that former President Barack Obama would tighten gun laws.
Central banks hold most of their foreign-exchange reserves in dollars, a boon for America that has allowed it to issue debt more cheaply.
Fast forward two decades and suddenly barbed wire and watchtowers don't seem like a boon to a waterfront that has a new baseball stadium, the state aquarium, the Tweeter Center concert stage and office and apartment buildings developing.
The rest of the year, the land would be a park, a boon to a city that has just eight acres of parkland per 1,000 residents, compared with 26 acres in Portland, Ore., and 31 in San Diego, according to the Urban Land Institute.
That was enough to send its shares soaring 4.8%, or 75 cents, to $16.25 in after-hours trading, a boon for a stock that has tumbled 68.1% in the last year.
President Obama's budget features more than $150 billion in alternative energy spending over the next decade, a boon that he claims has the potential to create 5 million jobs.
