Just been into my local Focus in Louth (it's in Lincolnshire). At the front of the store they had a pile of these space blankets. There was a poster with "Buy one get one free" on one side and "Buy one get three free" on the other. The person in front of me got about a dozen & the cashier acknowledged that it was three free. I don't need any because I used these type of offers last year to stuff the loft with this stuff.
The little rolls are better because they're easy to get through the hole in the roof, they're easier to handle once up there and they squash between the joists nicely. Space blankets are good because you're not scratching yourself for a fortnight after installing them.