Well - it worked until early July when it died. After much fruitless arguing with both Vodafone and the place I bought the card (including sitting in the shop refusing to move until they'd agreed to replace it), they exchanged it for another on 10 July. Which worked fine until early last week until it too died having exhibited the same symptoms as the first one. 2 hours on the phone to various people at Vodafone again today with no saisfactory outcome.....
These cards are obviously insufficiently reliable for general use....