We didn't feel the SuperPack's on/off switch served any purpose, since the only reason you'd want to attach the pack is when charging the device. Plus, the switch, too, is located in an obscure place, near the USB port, making it impossible to use while the pack is attached to a device.
When not attached to an iPhone or an iPod, the iPWR SuperPack has a top lid that covers its connector and USB port, which is useful for keeping dust out. Unfortunately, there is no convenient place to put the cover when the pack is attached to the phone. An option to clip the cover to the bottom of the pack would have been useful.
We tried the iPWR SuperPack with an iPhone 3G, and it brought the phone to a full charge (from completely dead) in about 2 hours. There is no battery gauge or indicator signifying how much juice is left in the pack, however. It only has a very bright green light-emitting diode (LED) that shuts off when the pack dies, or turns red after a full charge had been completed. The green light turned off when there was no more juice. Other than that, it stayed green all the time except when the pack was turned off or was being charged; then, it changed its color to red. The LED turned off again when the charging was completed.
The iPWR SuperPack is a compact, affordable, functional, and versatile extended battery. It's a good investment if you have multiple Apple handheld products, but it would be much more useful with a better port design and the addition of a battery gauge.