You can sync it via bluetooth to youtube or any other music source on your phone and immediately sing along with the music. You can turn down the volume of the singing (built in EQ filters that work really well) and turn up the volume on the microphone to hear your own voice louder.
The bluetooth connects really easily, keep your phone nearby though otherwise it may lose the connection. It has mini SD card slot for recording your songs (not tested yet) and charges via a simple USB cable, no batteries required! Bonus!
You can also add reverb effect to your voice which is a nice touch.
It also has a built in Radio Tuner so you can simply tune for Radio and sing along with that. Volume and mic volume button controls on the unit are easy to adjust. The previous and next button also manually skips forwards and backwards through the playlists on your phone, or will skip to next video on Youtube. Really useful.
I've already demo'd this with a couple of friends who have both asked me for the link in time for Christmas! A fun fun gift.