The classic Romanian deadlift using a barbell hits the muscles of the posterior chain: the low back, glutes, and hamstrings. And the dumbbell variation has some advantages over using a barbell.
Dumbbell RDLs allow for a larger range of motion since there are no tall plates contacting the ground. Sure, you can increase the range of motion by standing on top of a platform, but when extending the ROM while using a barbell, lifters often go deeper than they can control because they've been taught to target the floor.
They're more focused on how close they get to the floor than they are on maintaining alignment. This isn't the case when doing RDLs with dumbbells. The focus switches to maintaining alignment throughout the extended range of motion.