Mark is correct and not all understand the WHAT and WHY of seeking constant directivity.
Your gain would be totally dependant on your style of quality listening.
Early loudspeaker design, eventually was focused on a "coverage" goal. That is, in venues that had large spaces, dispersion/directing the full frequency response evenly over the largest area to be covered.
While this is a goal to even sound to more people at any place in a room or area, it IS NOT always the best goal for a High Performance audio use.
The upside to such wave guides is more even sound distribution no matter where you sit.
The downside, is that the you get more reflected sound and weaker/lower SPL's if you always listen "seriously" in a Sweet Seat.
If all your "serious" listening is done in that position, then your best bet is (with VMPS ribbon monitors) NO CDWG.
If you don't care about the sweet seat, and might benefit from the CDWG then go for it.
That said, due to the reduced specific output when CDWG is used you would need to change the caps to increase SPL's.
Aside from the fact that the WG itself blocks some output, the greater area of directivity reduces SPLs as you get further and further from the driver.
So the simple answer is:
If you always listen in the Sweet Seat = No CDWG
If you listen all over the room, or use the system more for Home Theater, then the CDWG makes sense.