I did a video about 6 weeks ago while in Colorado (yet to be published) where I say that the trap bar deadlift is one, if not the best lower body exercise.
It combines all the advantages of the squat and deadlift without their disadvantages.
The body is put in the same mechanical position as the squat, which makes it a great quads and glutes exercise. And involves the upper back and traps just as much as the deadlift.
The high handle allow you to use more weight which means more stimulation on the upper back and traps but a bit less emphasis on the glutes and hams.
The lower handle is a great way to build the whole lower body: glutes, quads and hams specifically. But since you use a bit less weight it doesn't overload the traps as much.