I have been using the BodyRez for a while now, and it is really a nice add-on for the acoustic. Especially live, when you don't necessarily have the option to split the signal to tweak the eq / rig to tweak as variedly.
In the studio I might prefer splitting the signal to get a wet/dry effect to tweak the sound myself, but that I haven't tested yet.
One thing that I would consider beeing either good or bad is that there is only on control for what the box does. It is of course a simple as it can be, but at the same time I don't have as much control over what is happening to the guitars signal.
But considering the price/sound ratio compared to buying stuff that does the same (presuming one can do the work with them / is pleased with what TC crew thinks you should be doing), this is dead simple.
Anyhows, this does make a piezomicced acoustic sound more natural, and I do think this is a good thing.