Greets!
I didn't wait for all the info to load (super slow dial-up), but assuming they only claim to improve DI (directivity, i.e. reduce off axis reflections) above ~2 kHz, then they should work as advertised, though they probably create more problems than they solve WRT the 'sweet spot' response unless their effects are accounted for in the speaker's design from the get-go.
Yes, horn edge diffraction has periodically been a 'hot topic' since the beginning of telephone design. Many horn designs don't need it though since their dispersion narrows with increasing frequency, so at the WLs where it would be an issue, the lens is 'out of the way', ergo there's nothing to cause any reflections till the frequency is low enough for standing waves to develop across them. This requires they either need to be terminated to an acoustically large baffle or rolled over or damped with foam/fiberglass insulation/whatever for best performance, which of course solves any potential edge diffraction problems also.
GM