Summary: For the price this sub is impressive. I have my amp and head unit turned down all the way and it is still way louder than I was expecting. Placed in a sealed enclosure with poly fill you will definitely only need one.
Conclusion: Unless your a total snob or trying to compete there is no reason why you should not buy this sub. The sound is great, I'm running a bridged channel from my Precision Power PPI P900.4 to 1 sub. In my rsx it sounds amazing. Its loud to the point you can feel it but wont rattle your car like a tin can.
Summary: So far this thing bumps... I'm using one of these in a slot port with a Kenwood Kac 297 I grabbed from a friend and man does it bump for the price. I have yet to break in the sub which I can only imagine will make it hit even harder than it already is.
Summary: Produces an amazing tight sound for the price. Just one is enough to have my ears ringing when I leave my car. When I get a new vehicle with a bigger trunk, since mine died two weeks after I installed the sub, I will definitely order a 2nd one of these.