They are both rated at 2200mah. From my experience of these powerpacks you can use your device while it is being charged. I have no direct experience of either of these packs and the best I can do is to direct you to this review
http://www.trustedreviews.com/periph...ble-Battery/p1

Another one that looks good is the Powerstick 15 rated at 4000mah but it costs $80. I am not clear if the small pin Nokia connector is included in the pack but it should be possible to buy an adaptor in a radio spares shop.
http://www.batterygeek.net/Batteryge...erstick_15.htm

If you have a few minutes, check out their Segment 1 and Segment 2 video demonstration. Not only informative but they also have a great chuckle factor, I still can't figure if that guy is for real or a spot on spoof.