I had a fairly expensive steam iron, which I bought ages ago, until very recently. The hard water around here finally put it out of action, so I had to buy a new one. With very limited funds available, I thought that I'd try the Tesco value model (which cost around �4). I certainly wasn't expecting much from it but it's far better than the expensive one ever was. (It's lighter, distributes the steam more evenly and makes ironing seem much less of a chore).
The Sainsbury's one is probably just as good. (It might even be the same model under a different brand name). However, if you're still in doubt, I recommend getting a 'Value' steam iron from Tesco.
Chris