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I have used them a few times but the change disrupts my accustomed form. The idea (which makes sense) is that the centering of weight, the more natural grip, and the kindness to a sore lower back permit you to pile more weight on the bar, thus stressing your body more.
I use a trap bar regularly. My reason is that, due to a shoulder "freeze" (that's what the doctor called it) I cannot reach back far enough with my left arm to hold the barbell for a squat. I perform trap bar deadlifts instead, which has some of the feel as the squat on my thighs and some of the feel as a barbell deadlift on my back. The key, as always, is to focus on proper form and not round your back.
It really doesn't fully replace the squat, in part because you can't go as deep as you can with a barbell squat.
I also do regular deadlifts, but not very often and definitely not on the same day as the trap bar deads.
I think that you do what ever works for you. I don't do bench press because I work out alone at home and don't want to take a chance on dropping the weight on my chest, I sub push ups for bench press. Rather than using the hex bar to me it appears the same thing could be accomplished using dumbbells. That is if you have lower back issues. The deadlift is used to strengthen your lower back but if you have lower back problems then maybe stay with lighter weights. I have injured my lower back muscle in the past but since I started following Rips deadlift instructions my lower back has never felt so good.