i use either the step on the rear, stand on the tire, or...open the rear door and fold down the seat. the hard backing of the seat makes a great step. I'm 6'3" or so, so it's a bit easier for me to load stuff on the top.
it is surely not as inexpensive but you know gobi makes a ladder for our rigs. some people have them on and are quite happy with them. i am reluctant because others claim the additional weight puts excess strain on the struts for the rear hatch. if someone posts a finding on where to get better struts or if gobi will include them with the purchase, then I am all over that ladder.
While I just use the bumper, backseat or tire, I can see the benefit of the step. It would keep your body centered over your feet and make it a bit more stable than leaning on the truck. But, it does drop you several inches below the top of the tire and then you have to pack it with you if you are going to need it to get stuff off the top at your destination.