Overall, I'm very happy with this product. My HTC Desire will always run out of juice just shy of the end of the day. And, of course, it's the point at which I'm commuting home in the dark and really need to know my phone is working. Having this with me is such a nice safety net and makes me feel much safer. It's a nice size, not too heavy, and the bag that comes with it is useful. The product is nice to touch. Feels like a phone in your hand.
I do worry, however, that the bag will come undone and I will lose the many connectors that come with the product. No doubt I wouldn't be able to find replacements for them and my investment will become useless. Also annoying is that the lights flash while it's charging...and keep flashing non-stop. I thought it hadn't charged all the way, but as it turns out, you have to press the button to see how far along it is in the process. Seems silly. Similarly, as you're charging your phone, it doesn't tell you when it's getting close to being out of juice until you press the button.
Still, even with these issues, this is a clever product that is very valuable, and I'm not sorry I spent the money at all.