You need to be absolutely clear before purchasing this - and it's not particularly cheap - what Apple products it actually works with:
It works FULLY with the iPad 2 and the iPhone 4S - and that's it!
With iPad 1, iPhone 4 and iPod Touch 4th Generation (but not 3rd or earlier) you can stream videos - and that is all.
I did not pick this up from the Amazon product description, so it doesn't work fully with my iPad (it's not a 2), but luckily I have an iPhone 4S, so it works fully with that.
I still think it is ridiculously expensive, but that's Apple for you!