Just tried the Fone Salesman 0.5mm card. It is indeed very thin except that there is a bulge at the top.
This has the effect of actually raising up the case near the camera more than the 1.3mm card I got with my CHOE charger. Apart from this the card is very slim and adds almost zero bulk. But given it potentially compromises the seal in the case more than a thicker, cheaper card, I don't think I'll be keeping it.
This of course is all just personal experience and opinion, others may find the card more suitable.
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