The reason I like it so much is because cheap portable battery packs usually pack under 1000mah of power. Thats not even enough to give you 1 full charge. And the more expensive 2000mah+ packs are often on the large side and well... expensive lol. On the other hand this little bugger is cheap and small enough to sit in my pocket without being a bother. What I find is the best part of it is the fact that you can choose what kind of AA batteries you put into it. I opted for Energizer rechargeable which are rated at 2450mah EACH for a total of 4900mah of power. Thats the equivalent of 3 G2x batteries. Keep 2 more batteries in your backpack/desk/purse thats an additional 4900mah. If that can't get you through the day you have more than just phone issues
Originally bought it for my Vibrant but quickly found it was awkward because the the product doesnt come with a cable adapter. This meant it was hanging and putting much strain on the usb port of the phone. Out of fear of breaking it I stopped using it. However since the G2x charges from the bottom there is absolutely no problem espcially seeing as I bought a 20cm micro usb extension cable so that the charger can sit in my lap or on a table while using the phone.
Just thought I'd share this since we can't get legit replacement batteries yet and even when they do become available they will cost a pretty penny. Got mine from Staples but they can be had on amazon also along with the usb extension able and rechargeable batteries.