Our house has several. Our HVAC guy was able to crawl around the attic and open/close some baffles to make a few of the hot rooms cooler, and of course we can close the vents in those rooms.
The problem is the cold room (furthest from the unit), which he couldn’t improve much at all. He suggested buying a booster vent to pull more air in.
I’m looking for any experience or opinions on how well these work. Here’s one I’m considering: