My good friend down the street has one, and it sounds great. I'd say at least as good as my Bose SoundDock, and likely better. 20 square meters will be no problem. Have you listened to one in a store nearby?
yea, i think having the option to run it off batteries is pretty cool.
i've listened to it in the store but it's a very different environment to where it will really be used. then again, i guess it can only sound better at home vs in a large shop with a high ceiling and lots of background noise.
I really wouldn't bother. It's very overpriced for the sound quality you get out of it.
If you need portability: the Logitech mm50 wins hands down for value. Under £70 (from Amazon), built-in rechargeable battery etc.
If you don't need portability: buy a hi-fi amplifier and some bookshelf speakers. You can get both for less than the price of the iPod Hi-Fi, and will blow it away in sound quality and is a better long-term investment. Budget for an iPod Dock if you haven't got one for the best sound output.
In fact, you can buy both options for the same or not much more than just the iPod Hi-Fi.
The iPod Hi-Fi / Sounddock can be beaten in terms of quality, and far bested for sonic imaging (since you can place the speakers apart) by a powered monitor costing £150. However after you've added a charger, universal dock and remote that's up to £220.
At this level, you won't be hanging in front of the speakers listening to every nuance so I say consider your use carefully. The 'separates' option may sound better especially to the audionerd but the Hi-Fi is more casually usable. It is however in my opinion fugly, but I use it more often than the powered monitor / dock. Don't quite know why. I just like using it better.