Not sure why they inverted the polarity in the ULF. I find this can create a disconnect between bass and mid range (our hearing is phase sensitive especially to 180 degrees changes in those lower frequencies as any one with a subwoofer can attest to and why all subwoofers have a polarity switch - there are also science papers proving this).
Looks like the transmission line bass has the Achilles heal of most TL designs - it is letting far too much higher frequencies get out - this will reduce mid range clarity.
https://www.stereophile.com/content/egglestonworks-viginti-loudspeaker-measurements
I agree with the philosophy - a large 12 or 15” woofer is only useable to a max of 500Hz. JBL large woofers (with the folded cones) go to 700 or 900 but they would break up in a controlled manner. I like Eggleston’s crossover points - they are close to where physics says they should be for optimal driver performance.