Hmm. So if you give these to people who, by definition, shop at ASDA from time to time, what you're saying isn't "do your shopping at ASDA", it's "don't do your shopping elsewhere". It's an attempt to retain customers, not to garner new ones. That's not generally good news for a shop, is it?
Tempting though it is to buy something 11% cheaper and then complain that it's not 10% cheaper, I don't think I'll bother. The reason I don't shop at ASDA is because their car park is harder to get into (and sometimes out of — I was stuck in it for over an hour once), plus their range isn't as good. Well, except for the Blueberry and Cranberry juice thing they have going on, obviously...