New day, new app in Cydia: WatchMob which will allow you to download any video from YouTube. The app is pretty straight forward and you only have 4 tabs to work with.
All you need to do is load the app and you will land in the Search tab. Search for the video that you want to download and tap on it. Next tap on the Downloads tab to see the progress of your download(s). You will find all your downloaded vids in the Video tab, where you can also play the video at any time.
Remember that you can find other alternatives in Cydia, such as YourTube or MxTube – apps that integrate directly into the native YouTube app on your iPhone or iTouch.
You can find WatchMob for free in Cydia via BigBoss repo