Pros * More than doubles the battery life (essential if you play games (Angry Birds, Uno, etc) that are power drains). * Protects your iPhone 4 from damage if dropped * Adds minimal bulk. I've tried other battery cases (including one with a cool "kickstand" for watching videos on planes and such) that turns the sleek iPhone 4 into a 1998-reminiscent brick). * Syncs with iTunes and iPhoto automatically when you plug in the USB to your computer. This also charges it - both the case and the iPhone. You never need remove the iPhone from the case to charge and sync. * Fits ANY iPhone 4 from either AT&T or Verizon * Cost: AMAZING value. It's better than any other battery-case for iPhone 4 and yet it is the most affordable.
Cons (only a small one) * Doesn't come with a little plug attachment that would let you charge directly into a wall socket (but the ones from Apple and for any USB device are compatible). So you must plug it into your computer to charge if you don't have one.
I've had iPhones since the day they came out in 2007 and the battery life tended to get shorter and shorter with each passing generation. I travel for work a bit and en route play a lot of games (Angry Birds, Uno) and also watch movies (two uses that really drain the battery fast).
I also tend to drop my phone a lot. iPhone 4's are very delicate, with their sharp edges and glass display. I knew I'd soon drop it and it would either shatter or one of the edges would get marred (and I hate when that happens).
To recap: The Lenmar Battery Powered Case for Apple iPhone was the perfect solution for my needs: 1) Battery extension 2) Protection 3) Minimal bulk 4) Ability to sync and charge without removing the phone from the case 5) Cost: AMAZING value and better than products more than double the price