Others who actually specialize in this movement could probably give you a more complete answer. However, I purchased a "Trap Bar" in the late 90's just for some variety.
I found the bar to be very useful and I agree with you, it seems to put more stress on the glutes and less on the lower back. I also seem to be able to do more weight with the Trap Bar. Although others have seen the opposite results.
I think (unless you are a Powerlifter) you should use both. Variety is the spice of life! I put it in the class of the Leg Press machine, which I also use. It's not as good as doing Squats, but it's a great piece for variety. I think variety is what keeps you training for many years, and perhaps what helps ward off injury.