YouTube Downloader App is developed by Red Kawa. Just like their converters, this tool is HTML-based, so you will find yourself using the application just like a website. Unlike other downloaders, YouTube Downloader App doesn't let you paste a video URL and download videos that way.
To download a video using this tool, you have to click on the "YouTube" link to go to YouTube.com and then find the video that you want to download. When you have found it, click on "Select stream", which will tell the application to go to the next step. You will notice that the stream field turns green when a video is detected. The next step allows you to set the download folder, the file name of the video that will be downloaded, and its quality. There are two options for quality: FLV and MP4. You can also set the application to add the MP4 file to iTunes automatically.
In my testing, I tried several videos and all I got back was a window saying that the video download failed and that I could consult the Help section to see what was wrong. The help section didn't offer any solutions.
All in all, YouTube Downloader App seems like a nice app. It would be great if it worked.