I have the Shark 250 watt system from gooddeals18 too. It's good bang for your $129 bucks. I have the 6" subwoofer, not installed yet, son is going to mount it in the trunk for me.
Sound quality and volume are good for this size speaker. One downside is there are no radio station presets... every time you turn it on it's on station 87.5 and if you want to listen to radio, you have to find the station. But I use it with my iphone. I also have Navigon GPS on my iphone, and the voice giving directions comes out of the speakers, too, as loud as your volume setting, and can be heard over the music.