These are fabulous winter tyres, we ran them two seasons ago on her diesel Golf and fitted them just before the really snowy weather of Dec2010. Epic performance in snow and ice. Felt really secure as our little lady was born in Nov '10 and my other half was extremely confident and couldn't believe how her car could effectively dig itself out of a snowy space with these tyres on (though I'm sure/expect other winters would have done the same).
We ran her Golf winters on a spare set of Pescara wheels, hence 225/40/18, and I used them on my Ed30 last winter, although in reality the winter was not as harsh '11/'12. That said the tyres did good, except when the temps were up in double figures, but 12/13 degrees C is not what they're designed for I guess.
The diesel Golf turned into an A4 Avant, so as I had a use for the 225/40 year old boots, we ordered another set in 245/40/18 and ran both cars, in the mild winter last year on these TS830P boots.
In my head, it's possibly overkill, that having these on can only help in cold weather.
For me the expense and hassle of storing/changing them etc is far outweighed by the security and confidence the right winter tyres can give you.
If you have found a deal on them, that's great, I bought them twice over so would certainly recommend these. Plus they always do very well in winter tyre reviews etc.