I own the 5DMarkIII and LOVE using this card. I spent the weekend shooting - Raws + small jpeg to the card, with my smartphone in my pocket and direct mode on the small JPEGS were going online as I took the photos. Necessary? Nope but certainly fun and worked like a champ. My small JPEG photos from my 5DMIII are just a tad better than what I would get with the Samsung camera.
- I have the 5DMarkIII and the EYE-FI and used it in the same way, works perfect, no complains.