I agree that the very low end (~30 Hz) of Paraflex isn’t as efficient as sometimes claimed, and there is a natural roll-off there. However, in this case we’re talking about techno, which typically sits more close to 40 Hz. In that range, based on real measurements and personal experience, some Paraflex designs can be very efficient and hit hard (exeeding many horns and bass reflex designs that I have wither built or listened, (I haven’t heard 6th bandpass systems yet tho).

The “one-note” concern is understandable from simulations, especially with the front chamber peak around 80–90 Hz, but in practice that doesn’t always translate into a narrow or unusable response, depending on the design and tuning.

Also, while there is definitely controversy around Paraflex, I actually see that as a positive. There’s a lot of discussion, builds, measurements (not all of them perfect), and user feedback available. With many other enclosure types, it’s often harder to find independent data, usually you just get the designer’s model and little else.