It's a great little cable. Works exactly as expected. Very useful in situations where you want to free up a charing outlet on your power supply or the pedal is too far to be daisy-chained from the power supply. Of course, you shall have a pedal which also has a pass-through feature. Most tuners and some other pedals do have a 9v out.
Also very useful in situations when you're trying out pedals and don't want to mess with power supply or swapping batteries. Just plug a pedal into a tuner and you're good to go at no time.