Why buttkicker?
The buttkicker allows you to feel the bass without rattling the windows, disturbing the neighbors, or waking up the kids. Also, medium to large sized rooms would require a lot of subwoofer (2 x $1k subs) to provide the "feel" that you get from a 10" sub in a 100 sq ft. room.
With the best buy price, you can add a second buttkicker and bracket to the kit for <$600. This is the low end of the price range for descent performing 12" subwoofers.