I don't know whether that is in room response or not. Those sort of frequency response specs can be misleading without more information. To bad there are no actual comprehensive measurements of this subwoofer to get any real idea what it can do in the 18hz extension mode. I'd bet it isn't really exciting.
With pipe organ, listening preferences and how loud you listen to is important. Pipe organ is very demanding and I would be concerned with mechanical/driver noise or even port chuffing with any of these budget subwoofers at higher output levels.
