As usual you can't expect miracles from mini-speakers. When they're that small, there is a physical limitation with what you can achieve with clever design and DSPs. Logitech UE opted against using DSPs with the Mobile Boombox, which makes it sound quite natural. The flipside is that there is very little low-end, and the high- and mid-range lack detail.
The Mobile Boombox does sound way better than any built-in speaker in smartphones and tablets, so it does have added value for mobile devices. That said, £79.95 is just too much for this product. There are more expensive models with similar specs, but they sound much better. Cheaper alternatives lack Bluetooth and are perhaps less advanced, but they sound just as good.
So if you're looking for a mobile speaker, we'd recommend only buying this Mobile Boombox if you can find it at a discount. For half price we'd say this is a best buy, but for the full price: keep looking.