RDLs can also be rough on the lower back. If you have a history of back issues or just need something a little more low-back friendly to balance out the other lower back intensive work you're already doing in squatting and deadlifting, do these.
They aren't regular trap bar deadlifts (which are more like a squat). Instead, think of it as a regular RDL, just substituting the trap bar for the barbell. You perform the first rep from the floor like a regular trap bar deadlift with some knee flexion, but from there it's a pure hip hinge pattern.
The trap bar lets you keep your hands more in line with your body, thereby reducing shear on the spine. It's very similar to using dumbbells, just with a far greater loading capacity.
One cue I like is to think about trying to reach your hands behind you as you lower down. You won't actually be able to do it, especially with heavier loads, but just thinking you will puts you in a better position and allows you to sit back into the hinge more to load your glutes as opposed to your lower back.