Thanks to a car accident 8 years ago I have terrible back issues. The ergo is awesome! I have even worn my 17kg DD while shopping and barely had a twinge! I can wear my much lighter DS all day and not have any issues.
I also have a hug a bub which is great for around home when I'm trying to get things done. I can't use this as long as the ergo though, as it does hurt my back after a while. But it's still better than just walking around holding him in my arms. I get terrible back pain if I carry him for too long in my arms.