These are quite nice pieces of industrial art. Fillet brazing was a popular technique when lugs didn't work (i.e odd angle frames, oversize diameter tubes, non-round tubes, etc.). That is one of the reasons why it persisted for so long on tandems. It freed the framebuilder/designer to explore new avenues prior to the development of internal brazing and the advent of TIG welding.
Its appeal these days is primarily aesthetic, a point not lost on a membership who prefers fancy crowns and sulpted lugs over Unicrown forks and and TIG weld beads. As already pointed out, these are massive fillets and are reminiscent of aero frames of the early 1980s. Consequently, they are much heavier than necessary and compromise the joint. There are certainly cheaper, lighter and stronger ways to join two tubes.
Even as art, I have some quibbles with these frames. The huge, aero joints don't work aesthetically when the bicycle is equipped with non-aero components. To my eyes, the sharp, pointed transitions from the stay ends to the rear dropouts, stand out in a jarring contrast of styles with the smooth, flowing transitions of the other joints. All the little touches, such as the exiting of the rear brake cable, rear derailleur housing and blind brake mountings are a little too complex and non-practical for my tastes, in what I consider should be an elegant but simple machine.
Of course, as art, it's subjective, personal opinion and as industrial art there's a melding of aesthetic and function for which each individual is going to have a particular blend that they consider ideal. Obviously, this mix is perfect for the OP and it's wonderful that he shows such enthusiasm for the brand. I can certainly appreciate his viewpoint and consider them quite nice, even though I find them somewhat disjointed and and the blend does not result in my ideal cup of tea.