This is a brilliant little cable, I bought it along with a boss TU-3 tuner and it powers most of my other pedals, (couple of overdrives, delay, tremolo, reverb, loop) saving money and space on my pedal board with individual power supplies.
I only have to use a separate power supply on my old electro harmonix memory man.
BOSS should really include this as a standard item along with their TU-3 but that little moan aside it really is highly recommended.
You can power up to 7 addition pedals, considering the cost of individual power supplies or a large pedal power system this is a really cheap and simple solution.
I have been using this for the last two years without any problems in a home studio environment, I'm not sure I would trust it for a gigging pedal board used in harsher environments but then again they are cheap enough to carry a spare.