I was looking for a card holder for 3 cards : (badge, metro-pass, credit card).  With sliding side shape, easy to use and secured, then i found this design :

https://pinshape.com/items/15687-3d-printed-credit...

Sliding shape is quite the same, and his design proved me that this principle work fine. I use same CC license Non Commercial, so it could be considered as a continuity or at least as an interpretation because of differents needs. 

By the way, thanks to Tony D, for all his sharing and vidéos.

As claims on this iteration, i've added an attachment point on top with a flexible shape, locking card but easy to bend when sliding up first or all cards,  and a covering shape in bottom to keep cards in place. 

Items on picture were printed with following parameters : 

PLA - layer 0.4mm - Top Bottom fill pattern : Hilbertcurve - density : 40% - Generate Support  (0h27')

finition : support for covering shape to remove