I got the Toshiba Flash-air when it was a $20 deal at Adorama. You cannot turn off the wi-fi on the card to save battery life. Also, once you set up the connection to the phone/tablet, if the camera powers down and then powers back up, the wifi connection to the camera is lost (on my iphone 4s at least) and you have to reconnect. Toshiba does have an app that you install on the iphone/ipad, not sure about android. The app is pretty simple, and I got it all set up and working in short order.
I haven't used it as much as I would if the feature was installed in the camera. My intent was to use it to add the Wi-Fi functionality to my G1X Mark I until I can afford the Mark II, just like on my 6D. If you get a good deal and do not expect to replace your camera with one that has wi-fi inbuilt in the near future, go for it. I tend to ride my technology to the bitter end, so for $20 it was worth it to me.
Never tried an Eye-Fi.