Yeah, Hong Kong is a very different set of considerations from simply, “modern street fighting.” Specifically, firearms laws there are far more strict than in the US, and the danger of running into someone using a gun is much lower than if you set your story in 1980s Los Angeles.
Obviously, if your characters are going up against the police, then that starts to become a serious consideration again, but for street level combat, there’s a very real probability that the people they’re fighting won’t have access to firearms either.
Now my knowledge on the subject is strictly 1999, so some of this may have been different under British rule, but my understanding is that under the PRC, arms smuggling is a capital offense. Possession of an unlicensed firearm is a serious felony that can carry a life sentence.
What little I can dig up from pre-1999, suggest that even before the British left, it was extremely restricted. You could own a firearm, but you not allowed to own, or store, ammunition. You needed to purchase, and use it, at the gun club, where you shot.
There were exemptions for people who dealt with large quantities of cash, gems, or other untraceable wealth, as part of their job. That may have persisted, I’m uncertain.
Within that specific context, yeah, I could see the tonfa being useful for someone dealing with street level crime. Ironically, they might be better off unarmed and using whatever they can find in their environment opportunistically, simply because of law enforcement attention. The full list of prohibited weapons is a bit vague in places. Near as I can tell, the tonfa isn’t explicitly restricted, but an officer might class it under one of those headers and arrest your character anyway.
Incidentally, while writing this, the thing that keeps coming to mind is Sleeping Dogs. This was a criminally underrated GTA style game set in 2012 Hong Kong, where you played as an undercover cop infiltrating the Triads. It’s a little off what you’re talking about, but is still a fascinating examination of the tensions for a character who’s operating undercover in a criminal organization.