I actually purchased the Eye-Fi two weeks ago but did not get to use it until recently. My original intention was to find something not as a replacement of my conventional CF card storage but an additional transfer to my macbook air during event photography as a safety.
First Impression
Comes with this weird looking SD card reader. Apparently, this reader is a must and that Eye-Fi does not recommend using another reader for this card, so don't lose it. The package is plain and simple just card, card reader, and instructions.
Installation
I am not sure how the installation process is for PCs, but for a mac it was very simple. It took around 10-15 minutes, and I had no problem getting the software into my mac and functioning.
Setting Up the Eye-Fi
It's quite straight forward. You will need to go on their site to get the proper setup for the setup that suits you most. Even with that said it basically only took 15 minutes in total for me to get the wifi transfer setup, and Ad Hoc Transfer setup.
Transfer Speed
I am used to shooting Large Raw, but I do not recommend using large raw for the Eye-Fi. The transfer speed is about 1 minute and 15 seconds for LRAW on a Canon 5D Mark III (22MB). For Event Photography I would recommend SRAW of MJPEG at the most. Because of this limitation, it may not be ideal for studio fashion photographers that like to snap away continuously. Mind you however, if you don't mind the wait, the Eye-Fi doesn't seem to have a problem with overshooting and when I tried continuous burst, although it took quite a while to transfer the files over to my MAC wirelessly, it got every single one of them.
PROS
Easy Installation & Setup
Straight Forward and user friendly application
smart phone compatible (direct mode, camera shoots directly to device)
My favorite of all is the Ad Hoc mode. Very useful when you are out on location.
Endless Memory mode is very useful. Allows user to set when the card delete photos by itself after it has transferred photo to your computer.
CONS
drains camera battery
very slow transfer (it takes about 15 secs for one SJPEG, but it may have been an issue with my slow wifi at home as well).
Only the pro version handles RAW and video files and also AD HOC mode, so make sure you buy the Pro version or else it's useless.
Card only has a capacity of 8GB, Eye-Fi should consider their Pro version to have targeted professionals that may require a larger capacity SD card.
WOULD I RECOMMEND THIS TO A FRIEND?
yes, but only if they have the extra cash to burn. Not cheap. $1000HKD for 8GB.

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If you are planning to use this for personal use, definitely save the cash and get the Yongnuo, I believe the Canon are too pricey for personal recreation. Even, for professional use, if you plan to move on to monolights in the near future (once you have a greater grasp of using strobes), these may be the lights to get. Let's face it, with the new 600 EX RT selling itself like a Louis Vuitton bag, you may as well save the money from the transitional phase of using a speedlite for a nice monolight head like a Elinchrome or a Profoto D500. I would not rely on these lights for event photography (especially if you are getting paid for the job). They may make a good spare speedlite for background or rim light if you already have reliable speedlites on hand. The price is definitely reasonable. Yongnuo has gone a long way and seems like their product although still lacking behind from the Canon's reliability, is catching up real fast.

