My 2 cents on the Harbeth (and other wide baffle designs):
The Harbeth speakers - the larger ones included - do a surprising level of "disappearing" as sound sources. Not what you’d expect from looking at them. So their design philosophy does seem to be working to quite a degree.
That said, Harbeths don’t "disappear" as sound sources as well as any number of other speakers that take the "dampen resonances" approach.
Thus far I’ve auditioned 3 brands of the wide baffle, resonating cabinet approach: Audio Note, Harbeth, Devore. In each case they disappeared more than their shape lead me to expect. But also in every case, that aspect was pretty easily bettered by other resonance-controlled speakers (e.g. my Thiels and others). In the wide baffle/resonating designs, I always sense some level of "fill in" between the sonic images. This can lead to a nice cohesiveness and richness to the sound, but can also become a bit more confused with more complex material, with a lot of instruments playing in the mix.
One of my go-to tests for this are some cuts from the Lost Angeles Guitar Quartet, in which 4 similar sounding guitars are simultaneously playing complex parts. The wide-baffle speakers I auditioned could make it harder to untangle one guitar from the next, vs my Thiels and some other low-resonance speaker designs.
The trade off is that wonderful bigness and warmth of tone from the wide baffle designs. I’ve really enjoyed what I’ve heard from Devore speakers which is why I’m contemplating buying a pair from the "O" series.
