It might seem strange to have a rechargeable battery for an item that already contains a rechargeable battery itself - but over the last few years I can't say how many times I wish I had had this item! There have been many occasions when at a crucial part of a game, where many hours of play had built up to this point - only to be confronted with the message that the controller was running out of charge.
The thing is that the lead to the controller from the PS3 is too short to be used in play and you can't charge while the PS3 is turned off - so the temptation for most people, (especially those who fit in gaming around other life events) is to just pick up the controller and play, without thinking about charging, with the inevitable result.
What this device means is that you can play a game at the same time as charging the power bank - so that when your controller runs out - you can fit the power bank and carry on, without having to stop in the middle of a game. It fits very neatly and is quite light, so you don't notice it when in place - it looks exactly like the material and branding of the PS3 controller, so doesn't distract your eye, either.
All in all, this is a great product for the lazy gamer, who wants to spend all their time playing - not waiting for your controller to charge. The only thing is - where has this been all the years when I really needed it? Now we have the PS4 and the PS3 is presumably at the end of its life, so I'm not sure how timely this is and hence how useful it can be? But I will certainly use it over the next few months and be glad of it.