This is my second portable battery, and it's as equally useful as the previous one I had brought (http://www.amazon.co.uk/New-Trent-iCruiser-IMP1000-Blackberry/dp/B004CHMP50).
The ACD66 weighs about 190g, as opposed to the IMP1000 at 280g. This is fine, as the ACD66 is about 2/3rds the weight and capacity of the larger unit. The unit has two outputs - 1A and 2.1A. Although the 2.1A is meant to be for tablets and the like, there is nothing wrong with using the 2.1A for phones, as they only draw the amount of amps they need. Therefore, this unit has a distinct advantage over the other battery I have, as it can charge two phones at the same time. A downside is that this unit can only be charged via USB - this does take a long time so best to do this overnight.
Another nice benefit of this battery is the "telephone cord" type cable which comes with it (see uploaded photo) - this is great for using when travelling. The LEDs have plenty of different states, so it is easy to approximate how much capacity is left in the unit. The unit is very shiny, so this attracts fingerprints easily. I'd have preferred the whole unit to be a matt slightly rubbery texture as the base is.
Overall this is a great battery, and would make a great gift for someone who is into their technology, as it really is very handy.