First thing you need to understand is that 1 watt, when it's done properly and put through a decent cabinet, is loud. You can drop the output down to 0.2 of a watt though and if you want to keep on the good side of your neighbours you'll have the voulme control set to about 3.
It's a qaulity amp. It's built to last and looks cooler than a cool thing on an iceberg. The chances are though that you are going to buy this because you're a Marshall fan and will buy one of these 50th Anniversary models even if it sounded like a cat with a red hot poker up his bot. It's a bonus though that it actually sounds pretty good.
If you keep it in good nick you're probably going to get back what you paid for it and, in a few years, maybe a little more as Marshall are producing these for this year only.
In conclusion. At £479 it's not cheap but it does sounds good, it looks good and it's going to keep its value.