The interesting for me (as advertised) function was the mechanical protection - The buckling and breaking in the back pocket. This seems to work quite reasonable (but a bit the shells turn also), but the cards are sometimes hard to get more out of the sheath. In my debit card I have to open each time, push sideways and initially separated by the finger on the card in the envelope of the walls, because it seems there stick the envelope. Interestingly, I have this problem with my credit card - why this is, is beyond my knowledge.
Nevertheless, it makes the product at least for some card virtually useless, since you do not always have a few minutes to get the card out of the envelope.