While I great enjoy my digital rebel, the view finder (due to it having a pentamirror, not a pentaprism) is dark, and it is small. The small size makes it harder to see how well focused things are. And then when you try to do it indoors when the view finder is already dark, it is near impossible to get an accurate focus.
If that device lightens things up, that would be awesome. If it lets you zoom in to verify the focus, that would make it a needed addition to my camera bag. I'm guessing it will cost about $170 here in the U.S..