i think there are a couple of things being mingled here that possibly shouldn't be.
1. The Bridge Doctor being used to correct excessive sound board belly-ing is a valid repair, without a doubt. It does what it is supposed to do, and what it is advertised as doing. It also adds weight and rigidity to a place on the guitar where it is potentially an issue. Weight, because the Bridge Doctor does weigh something. Rigidity in that it is straightening out the belly-ing because it mechanically forces the belly-ing to straighten out. It is a mechanical force that is pushing the soundboard into a less bellied/straighter position. The dowel that pushed against the bottom side wall of the guitar does add rigidity. What the end sonic result are is debatable, in my mind. The added weight may have an effect, the added rigidity must as well. All of that may be swamped out by the sound board regaining its "normal" shape. I have heard both things happen. In all cases, the belly-ing was reduced. In some cases, the guitar sounded a little bit better; in other cases it didn't (mostly tending to reduce upper end and increase the bass, could be good or bad depending on if you wanted the increased bass relative to the midrange and high end). Easiest way to see the effect is to weigh the Bridge Doctor (all parts including screws), make up something with close to that weight, and attach it with self stick tape to the bridge. It won't duplicate the rigidity increase, but will give an idea as to which way the sound will change. I call this a valid repair, because the replacement of a bridge plate is a non-trivial task; the luthier is working blind, using a sharp instrument (a doubled back chisel) that is running against the bottom of a high stress area of the soundboard. A great deal of care is called for, or damage to the sound board will result.
2. When Breedlove was using the Bridge Truss, they designed the guitar to work with the Bridge Truss in place. As they themselves said, it allowed them to use a thinner top, and (I am speculating here, I haven't run into any Breedlove guitars) most likely altered the bracing to also accomodate the Bridge Truss, and get the sound that they wanted with the Bridge Truss in place. This is not the same as it is for a guitar that was never designed to have a Bridge Doctor. The tops and braces were never designed to accomodate a Bridge Doctor, so were never optimized for its use like the Breedlove guitars that used the Bridge Truss were.
These really are two separate cases, and don't really relate to each other, except as basic concepts. One is a standard guitar, the other (Breedlove) that is designed from the ground up to use the Bridge Truss (i.e. Bridge Doctor) as an inherient part of the overall guitar design. I don't think that the sonic end results will have anything in common.
1. The Bridge Doctor being used to correct excessive sound board belly-ing is a valid repair, without a doubt. It does what it is supposed to do, and what it is advertised as doing. It also adds weight and rigidity to a place on the guitar where it is potentially an issue. Weight, because the Bridge Doctor does weigh something. Rigidity in that it is straightening out the belly-ing because it mechanically forces the belly-ing to straighten out. It is a mechanical force that is pushing the soundboard into a less bellied/straighter position. The dowel that pushed against the bottom side wall of the guitar does add rigidity. What the end sonic result are is debatable, in my mind. The added weight may have an effect, the added rigidity must as well. All of that may be swamped out by the sound board regaining its "normal" shape. I have heard both things happen. In all cases, the belly-ing was reduced. In some cases, the guitar sounded a little bit better; in other cases it didn't (mostly tending to reduce upper end and increase the bass, could be good or bad depending on if you wanted the increased bass relative to the midrange and high end). Easiest way to see the effect is to weigh the Bridge Doctor (all parts including screws), make up something with close to that weight, and attach it with self stick tape to the bridge. It won't duplicate the rigidity increase, but will give an idea as to which way the sound will change. I call this a valid repair, because the replacement of a bridge plate is a non-trivial task; the luthier is working blind, using a sharp instrument (a doubled back chisel) that is running against the bottom of a high stress area of the soundboard. A great deal of care is called for, or damage to the sound board will result.
2. When Breedlove was using the Bridge Truss, they designed the guitar to work with the Bridge Truss in place. As they themselves said, it allowed them to use a thinner top, and (I am speculating here, I haven't run into any Breedlove guitars) most likely altered the bracing to also accomodate the Bridge Truss, and get the sound that they wanted with the Bridge Truss in place. This is not the same as it is for a guitar that was never designed to have a Bridge Doctor. The tops and braces were never designed to accomodate a Bridge Doctor, so were never optimized for its use like the Breedlove guitars that used the Bridge Truss were.
These really are two separate cases, and don't really relate to each other, except as basic concepts. One is a standard guitar, the other (Breedlove) that is designed from the ground up to use the Bridge Truss (i.e. Bridge Doctor) as an inherient part of the overall guitar design. I don't think that the sonic end results will have anything in common.