I have been very disappointed with this product. First, my background. I consider myself an expert on transmitting on the Nikon. I've been doing it since 2002 even before Nikon provided a solution. I was using a battery powered UHF transmitter and receiver using the video out on the DSLR's. I then went with the Nikon's first wireless camera D2H, then WT3A on D200 and then WT4A on D300. I thought this sounded like a great option. I bought it to use on my D7100.
When conditions are PERFECT, then this works great!! But I do a lot of event shooting. If you find yourself at the ballgame, or church where there are lots of people with Mobile phones, then you can forget ever getting this to work. With lots of signals from other cell phones, it's impossible to get this working even with the iPhone or iPad up close to the DSLR. Once everyone starts leaving it will start working reliably again. Even then it's not reliable enough to depend on it. It disconnects so often, I've only been able to get about 12 photos transferred before it disconnects and I have to start all over again. I will say, I did use it a lot on my recent trip to Germany. I uploaded 400+ photos to it. But remember to only load less than 20 at a time and ensure you are away from lots of cell phone signals. And realize that you can't have your phone more than a few feet away from the camera.
In Summary, for $50, it's probably worth it to play with it as long as you realize the hassle this will be. On the other hand, spend the $900 and get the WT5A transmitter if you want reliability and for it to work right each and every time. I am rethinking using this with my clients. I currently give them my iPad and use the WT4A to transmit ALL of my photos as I take them. This works very well. This allows them to review the photos and Tweet immediately and post photos as the even takes place. I don't see this working with this cheap product. First my WT4A transmits as I photograph with no interaction on my part. The WU1A requires me to change how I work. With it on, I can't preview photos on the camera. The phone, must manually select the photos to download. It definitely has slowed me down using this product.
I think it's a good idea, and for $50, definitely worth getting and trying it out. But do not expect this to work in a professional situation unless in a controlled environment.