The Romanian deadlift hits the low back, glutes, and hamstrings. This classic hip-hinge movement is a great strength and muscle builder, and the dumbbell variation has some advantages over using a barbell.
High-rep dumbbell RDLs allow you to go through a larger range of motion than what occurs when using the barbell with plates. Sure, you can increase the ROM when using a barbell by either using smaller weight plates or by standing on top of a small platform. However, when extending the ROM while using a barbell, people tend to go deeper than they can control because they've been taught to target the floor.
In other words, they're more focused on how close they get to the floor than they are on maintaining their alignment. This association seems to go out the window when performing RDLs with dumbbells and the natural focus switches to maintaining alignment throughout the extended ROM. Give them a shot!