However, the ATV Pro did NOT work with my MacBook Pro, my Samsung PC, or my new iPad. It appeared to me that the ATV Pro is strictly for the Apple TV. So, I spoke with the manufacturer, and while they report it working with HDMI sources like a Mac mini, a Blu-Ray player and similar gadgets that are AC powered. Kanex told me that, since their ATV Pro device isn't powered, it needs a 5 volt power supply from the HDMI source, and it appears that laptops and the iPad don't provide that.
The Accell UltraVideo did indeed work fine with my MacBook Pro, my Samsung laptop, and my new iPad using Apple's HDMI connector. But audio is not transmitted so keep that in mind. That might be fine for presentations, but not for entertainment purposes. The Accell UltraVideo does indeed require power, but it can work using the included USB cable and a USB power source, or the provided USB power brick.
The Kanex ATV Pro packaging is elegant, but to be fair, they need to include less in the package, since no power brick is used. It's an easy gadget to take with you, as long as you only need to connect to an Apple TV. The sleek design of the gadget and the package would make it right at home in the Apple store.
The Accell solution is more powerful, although the packaging is bit clumsy with all of the separate cables and components, and the blister packaging. I would like to see a cloth bag or case included to make transporting it easier by keeping the power cable and brick close together. I do like that the HDMI cable is separate, so you can use a longer cable if desired.
To summarize, it's a split decision. Each device has its purpose. The ATV Pro is great for use with the Apple TV when you need to connect to a VGA output device, plus you can connect the audio to your projector, speakers or other audio output device. If you need to project from your iPad, you can use AirPlay and wirelessly send audio and video to the Apple TV, and then use the ATV Pro to connect to a VGA display. The unit itself is sleek, small, and works great as long it's used with an Apple TV. I recommend the ATV Pro for office conference rooms where they have a traditional VGA projector and want to add an Apple TV. It can be a great solution for anyone in the office to quickly, and easily wirelessly project from their iPad using AirPlay Mirroring.
The Accell UltraVideo is extremely versatile, and it worked with every HDMI source I tried. You can project directly from an iPad using Apple's HDMI connector, on a typical projector with VGA input, and still keep your iPad charged using the 30 pin charging cable. I will be keeping an Accell UltraVideo adaptor in my gadget bag so I can always present on any projector, from any HDMI source, with no worries.