The 5D III does support the Eye-Fi card (in it's SD card slot) and the iPad also supports it. That's not a problem.
The problem, is that if you shoot RAW (I prefer to shoot RAW) it is painfully slow to transfer images via the Eye-Fi.
The radio in the card is not continuously active. It stays off while you're shooting (to conserve battery power since the radio drains battery faster) and after about 5 seconds of the camera being idle, the radio will switch on, join the network, and begin transferring images. JPEG images transfer in just a few seconds... but RAW images take considerably longer (probably at least 30 seconds for each image but I've never timed it.)
That means you "shoot" and wait for about the next 40 seconds for your image to show up on the iPad... which is painfully slow for proofing before moving on to the next shot. And as I said... it's not like you can ignore it and just keep shooting while images transfer because it will never shoot and transfer images at the same time. If it has a bunch of images queued up to transfer and starts copying them, as soon as you start shooting again it will halt the transfer and switch off the radio (it will switch on again when the camera goes idle again.)
So while this "works" in concept, it's painfully slow to the point that I don't think you'll enjoy it.
ANOTHER option (and I haven't tried this myself) is to use the Canon WFT-E7A wireless file transmitter for the camera. Canon also has a WFT Server app for iOS that would work on the iPad and allow the WFT module to transfer files to the iPad that way. See: http://learn.usa.canon.com/app/pdfs/quickguides/WFT_Server_iOS.pdf
Before you race out and buy one, read the product reviews. Lets just say it doesn't exactly get stellar reviews. From what I can tell, it "works" in that it does what it claims to do, but it's described as being extremely clunky. Add to that ... it's ludicrously overprice for what it is. If you read the reviews you quickly get the idea that Canon basically crammed something out the door without much thought to it... and should probably be embarassed by this particular accessory.
I like my Canon products... but even I had a hard time with the price tag and the fact that it's appearance suggests it was designed by a team who was not allowed to know what the 5D III actually looked like when they were designing this accessory.
Tim Campbell
5D III, 5D IV, 60Da
