The cylinder subs don't take much floor space. If they work in the room, they can almost disappear. My SVS PB-12 NSD is behind a chair that sits in the front of the room and is nearly invisible despite it's huge size.

Physics plays a large part in subs. The bigger they are, the more bass. The more power, the bigger the bass. So, small subs must be very powerful (expensive) to match a large sub that has less power.