The medium lady dior ( in the ad with Cotillard ) is not very large and you can put only few things : wallet coin purse , keyholder , small cosmetic pouch , that kind of stuff . Go and see the movie ad , you'll see quite well Marion Cotillard's hands compared to the purse .
If you are used to a speedy bag size full loaded , with a lot of stuff , I suggest that you purchase the large size or even the shopping size which is 100 euros more only .
Hope I have helped you .