I was recommended this product by Chris Dodds and Dave Shumway. I was trying to find the best way to track moving objects while shooting video with a DSLR. The inherent problem with shooting video on a DSLR is mirror needs to be closed for the live view to be on. This means you can't look through your viewfinder while shooting video. This introduces a lack of stability while your shooting.
So the answer is using a product like the LCDVF to make your LCD become your viewfinder. I also tested the Zacuto Z-Finder 3x and found it to be fantastic as well. The Hoodman HoodLoupe is also an option, although I have not tested it.
Each of these products magnifies your LCD and allows use like a traditional viewfinder. I have to admit I was a little confused when I first read this. I'm thinking, OK.. My LCD is already 3" and my face will be right up next to it, why would I need it any bigger? The answer is, you just do..! The LCD looks like your viewing a 42" TV. You can see down to the pixel and ensure your getting correct focus. The LCDVF has a 2.5x magnification and the Z-Finder has a 3x, so the advantage goes to the Z-Finder on that one.
The real reason you want to use this is to give stability to your handheld video. But the Z-Finder is also more than double the price and includes a large bracket just to get it to attach to your camera. The LCDVF uses a simple but genius magnetic ring around your LCD, then you just put the LCDVF up to it and "click" it locks in via magnet. The magnet holds it in solidly, but removes just as easily.
The last feature I'll mention is the diopter. The Z-Finder has a diopter that can adjust specifically to your eyes. The LCDVF does not have this feature. I do not wear glasses or contacts so this was a non issue for me.
Another use for a LCD viewfinder is for more accurate review of images in the field. This is always useful to make sure your nailing the shot.
I chose the LCDVF for the price and ease of use. I do kind of wish I had the 3x, but the 2.5x works fine. So mine looks like a 37" TV instead of a 42" =)