I purchased it from ebay for the princely sum of £9.99 including delivery and it arrived in about 3 weeks from China. I opened it up to have a look at what's inside and there's a 5v regulator and a 12v regulator that should be good for about 2A each and what appears to be an 1800mAh 3s lipo battery. It also comes with a charger and a male to male barrel connector that fits most CCTV type equipment. It has a pretty low self discharge rate and even after a few weeks without use it still seems to be holding it's charge well.
This has turned out to be one of the best little gadgets that I've purchased in a while and is a really useful item to keep in the flight case. I've used it for testing a variety of FPV equipment including cameras and screens and also for emergency charging of mobile phones and other USB devices. If like me, you have one of those little keychain cams then you can use it for charging those and I also use it for keeping my video goggles topped up.
I really wouldn't be without it in my flight box now.
Pros: Price, Dual voltage output, size/weight
Cons: None that I can think of