Just did a little looking around.
For the OP - The Amstron PP33 has a max output of 700mAH even though the storage capacity is much higher. The PP33 is also a lot bigger than the Kensington. There is a one year warranty on the PP33. I think 700 will work with a pass-through, but I'm not sure.
For Lucky - Looks like a nice unit. I like the case, but there is no brand listed and I couldn't find any warranty. The max output is 1A or 1000mAH. The capacity is higher. Capacity and output are two different animals.
For the rest - The Kensington has a max output of 1.5A or 1500mAH. It has a two year warranty.
I like the one that Lucky found, but I very much like the warranty on the Kensington. So much so that we bought three (3) at the sale price. Figure we got 3 for the regular price of 2. Plan to rotate the third one in regularly. I don't know enough about electronics to know if the increased capacity will actually make the units last longer between charges, but I believe that to be the case. I still think the Kensington is the smallest. It is no more than 1/4 inch (if that) thick and maybe 2 x 3.5 inches. I think it's actually smaller than my iPod nano (2nd gen). It also charges on RAZR (mini usb) car charger.