Often more drawbacks than advantages.
As said above, all-in-one systems often have more disadvantages than advantages unless the technology is stable. However the only real advantages are often cheapness and space saving.
In the product for which were commenting on. By having the speakers(there is no comment if there using standard plugs on 'em) Amp and DVD player all togeather you risk replaceing the whole lot because of a fault or a required upgrade.
For example I have had expensive amps and DVD players over the years break on me, and I can quite happily say that whilst its no fun, at least I was able to spend £120 replacing my DVD player rather than replacing the £650 DVD player and the £800 Amp as it was at the time.
This product happens to be quite cheap, and at some point all-in-ones vs separates become mute.
The key issues when deciding to go for a product like this are:
1. How long do I expect any part of these components to last?
2. Is there any new technology coming that might shorten the life expectancy of the equipments useful function?
3. What benefits do I get from an all on one system ? (a single remote control might be one)
4. Can I add other bits on? (for example does it have AUX in, allowing 'things' to pluged in, in this case yes it seems to)
For the price they seem to be asking, I suspect most people will be quite happy presuming the sound quality's good and robust. As it will give the same sound quality (maybe better) than you get from low end separates. I feel when your looking at over £400 for an all-in-one system you should consider have already considered the alternatives (and done some listening in audio test rooms).
-sin