Have to get that guy they debunked every electric guitar in existence as well as all the most popular amps and determined that literally nothing people thought led to the sound characteristics was true. I forgot how the amp worked out when he made an amp that could replicate the models he tested, but the electric guitar came down to pickup position along the strings and distance from them. Six strings strung along a gap between two tables could replicate the sound of any guitar by having the same pickup location.

I would assume the body of the guitar actually does something on an acoustic though, but people made that assumption about electric guitars for as long as they have existed.

Having played a few of these, yeah, you hear it a little better as the player. They don't sound that much different out front.

If you think about it, on an acoustic guitar the top of the guitar is the "speaker", driven by the vibration of the strings through the bridge. That thin plate drives vibration of the air it's in contact with on both sides, front and back. The vibrations from the front are desirable, because you want the audience to hear the guitar, but the sound projecting back is only useful to the extent you can reflect and redirect it with the body cavity and sound hole(s).

So yeah, to the extent that sound coming out of the side of the body is useful, these make a difference. It's up to you if that's actually important to you though. IMO these are less useful for performance situations, more for people playing for themselves (practicing, etc.)

It might give you a kind of “natural monitoring system” for small gigs? As a player you will hear the guitar body amplification through that hole more than from the front I guess .