Hi John; I've now installed four Bridge Doctors in a variety of instruments, including a Rob Armstrong mandocello and a really good old Martin D18. One was mine, the others were customer jobs. If anything the response improves, as the design of the Bridge Doctor acts in a similar way to a violin soundpost, the top flattens so the bracing works properly, and the proper break angle of the strings over the bridge is restored. This is confirmed by the satisfied owners. Have you heard a guitar with one installed? Breedlove install them as standard in all their high end acoustic guitars, as this enables them to use lighter tops, and as I'm sure you know, lightness usually equates to more resonance. McGrath of Harlow also has some experience, and reckons it saved his old guitar.
Tim