The Bicor 20 is an interesting design; it's not a horn per se, more a hybrid multi-chamber approach. Since Lowther don't publish the plans, hard to say what performance will be like with any reasonable degree of certainty.
The Alerion was, as I recall, a custom enclosure for Lowther US by the late Terry Cain. From the appearance, I suspect it had a similar configuration to his Single BEN, but plans have not, AFAIK, been released, and knowing Terry, he probably tuned it to use the particular resonant properties of the construction materials, which were custom laid up in his wood shop.