Thanks, CG ... she's quite good, isn't she?
The ToneWood Amp apparently is self-powered, and simply mounts on the back of the guitar. It then picks up the sound wave from the guitar, and amplifies / modifies them back into the body. It allows the guitarist to add a some extra volume, as well as a few basic effects, like reverb, delay, tremolo, etc. I don't much more about them, but here's link to their site for more info. It looks like a simple & portable way to enhance a performance, without a bunch of extra gear ... worth investigating.
https://www.tonewoodamp.com/