back row is a great exercise for developing good muscular shape and strength for your back. whether you do it with dumbbell or cable, you are going to incorporate lots of small muscles that rarely get used, and also work on a lot of big muscles in your core area and back. there are variations available for doing this exercise but make sure the safety notes are kept in mind.
make sure you control the weight and do not bounce it, make sure you keep the back straight and flat, do not bend the neck, do not grab the dumbbell or cable with tip of your fingers, and stretch your hamstring before doing this exercise if it is tight. make sure your breathing has a rhythm, so breathe in when you lower the weight and breathe out when you pull it, but make sure you keep the core steady all the way through the exercise.