It’s called a Handheld Home Theater by its creators. The Belkin Thunderstorm is basically an iPad speaker case that produces great sound and integrates with the iPad.
With the Belkin Thunderstorm, the speaker is always there, ready to go, and the form factor makes it easy to take along with you. The speaker also comes with an application that allows the user to control many variables of the sound. That comes in handy for all of your different music.
You have to use an external power supply to charge it, but it still seems like it is a pretty nice device.