What a kettlebell is good for
The weight of a kettlebell hangs below the handle, so it wants to swing and pull rather than sit still. That makes it the obvious tool for hinge patterns and for work where the hips drive and the grip, the core and the lungs all get taxed on the way.
One bell goes a long way, but the jumps between sizes are large. For slow, heavy, controlled work a dumbbell is usually the easier tool.