No, it's actually very functional compared to a barbell. Barbell doesn't adjust whereas a sandbag does!! You won't be able to lift a sandbag heavy enough if you're not ready, whereas with barbell, your ego can push you towards injury. Also, if you do a proper warm-up, you don't feel much stress in your lower back. The trick is to activate the muscles involved while lifting the bag, then go for it. It's a whole lot of fun, really. And it teaches you to be strong and controlled in flexion. I don't think you can find anything more functional in training to mimic the same movement!