I have the Zaggmate and I’m very happy with it. I can’t speak to the usb thing as I haven’t had to charge the battery. The case is not my primary case. I use the InCase Book Jacket close to 75% of the time and the Zaggmate the rest and which I chose depends entirely on how I anticipate using the iPad at the time I’m packing up. The Zaggmate does not let me use the iPad the way I tend to across the entire day when I am out and about which is why it is no good as a primary case. I do a lot of writing on the iPad, though, and some data entry here and there, and for that it’s fabulous. For life out in the wild, it goes back into the Book Jacket. The Zaggmate offers zero protection when you are using it as a keyboard/stand combination.
If you don’t yet have an iPad at all, my recommendation is actually to not get ANY case for a few weeks until you figure out how you are going to use your iPad. I *intended* to use mine just as a reading and writing tool, but it was so good at other things that I found many, many other uses for it. (I used a Domke camera wrap for protection until I made my initial case decision. A padded envelope will also work.) By waiting, I discovered I hated the idea of having to open anything up (like a laptop opens), unzip, or unbuckle my iPad to check it for 30 seconds. Drives me nuts. Knowing that about my own habits would have easily eliminated some of the choices between cases you are trying to make for yourself, were I now trying to choose.