sorry but this item is rubbish. it is most certainly not fast and efficient. it takes 3 times as long as the original charger which came with my iphone. ie an hour and a half for a full charge from zero. i thought it must be faulty and was sent another one but it is just as bad.
I bought this because it was advertised as : GENUINE APPLE NEW IPHONE 3G USB MAINS CHARGER - BULK PACK. It has a picture of a plug, so I was expected to get a spare plug and cable. What arrived was an iPhone dock, which wasn't what was advertised, not what I was expecting. I thought, well, if it works that'll be OK. But it doesn't work. It isn't compatible with iPhones. The iPhone just pops back off the dock station and won't quite connect to charge unless you hold it on... not quite practical really. I have also had no response from the seller about how to return it, nor any apology, and it's still advertised as being an IPHONE 3GS MAINS CHARGER BULK PACK, so all in all I'm not that impressed.
This product is advertised as compatible with iPhone 3GS. well be very wary. It's not! Read other comments too as others have had the same experience. If only I'd read the comments too. I only wanted a spare charger.