I have a feeling someone's unreasoned prejudices are continuing to give ex-battery birds an unfair bad name. Shell problems probably have far more to do with an ignorant amateur getting the diet wrong than anything intrinsically "wrong" with the birds - for someone on a budget, given the choice of shelling out (intentional pun) £100 or more to get a few pedigree birds, and 50p a head for ex-battery birds, there's every chance that they may not be able to afford to give pedigree birds a home at all.
As for the "argument" that not having ex batts will somehow stop them being bred is utter nonsense - the batteries will buy the birds come what may, all we are concerned with is what happens to them when their dreadful time in an animal Belsen is over. After having been poisoned, cramped, overheated, and likely had chunks of their beaks burnt off, of course they are more likely to suffer an earlier death than a "pampered from the egg" pedigree. I could rail about the problems common to any "overbred to show standard" animals, but won't...
The fact remains that for many people giving a few ex-commercial hens a pleasant retirement is a good, viable, and moral choice, which should not be rubbished - there are just as many reasons to not go for pedigrees - live and let live!