Arthur: Not something you need often, but when you need it, it's absolutely indespensible! I used the WFT-E4A IIA shooting 3000+ pictures in a weekend at a horse show. I was shooting pretty much continuously, while my assistant was at our table with a laptop showing people shots. Immediately after each event, they could go over and review the pictures. No more juggling memory cards or waiting hours to view the shots. It more than paid for itself in sales there. Setup can be a little tricky. If you don't shoot RAW, you could just use the EOS Utility software that came with the camera to bring the pictures over. This is relatively quick and easy to use. If you shoot RAW, as I do, however, this takes too long (~17 seconds per shot). In order to keep RAW and jpg on your card but only send the jpgs across the network, you have to use the FTP transfer mode. To make this work you have to set up an FTP server on the network and get the WFT-E4A talking to it. I used Filezilla server (it's free), and it worked just great, but if you're not familiar with FTP and servers it could be very daunting. I definitely recommend getting the device a day or more before you need it so you have time to set it up and try it out before you get on-site. Once you have it set up properly, however, it works like a dream. One battery lasted all day - over 1500 transfers - without any problem at all.