Like a typical dog clutch. I can see just the slightest bit of taper to the teeth, to be tight and take up any wear over time. Good design. I might have put some radius at the bottom of each inner corner, but I'm sure the current design is completely adequate.

The lugs on each outer side, I could easily see that being brazed to a chrome-moly steel frame, just like traditional lugs, even with a welded frame. Although that would most certainly damage the original paint. What I wonder about is, how is it attached to an aluminum frame, bonded (epoxy), or if that is only suitable for steel frames? Same question for carbon, although a) I doubt a carbon frame for touring, and b) torque couplings negate the weight savings of carbon if someone was traveling with a racing frame.

If I recall, some quality brand frames about 30-40 years ago were bonded tubes into lugs, but problems showed up over time.

I'll also add, folders typically have fail-safes, secondary latches, to prevent coming undone while riding. I don't see one on the coupler above. I would have designed a spring-loaded collar or lever that engages the spanner wrench cutouts, or an additional part that can be added to lock things. Or at the very least, once put together, put bright nail polish on both sides of the interface (should stay close position each time), easily seen when riding, as a quick check.