TVC preamps: good or bad?


I was wondering what the advantages and disadvantages are of a TVC preamp? I have read elsewhere that transformers introduce coloration and aberrations in the frequency response, which is why we try to get them out of the output stage of valve amps. But ... what are the pros and cons of TVC preamps?
amfibius
This thread is a bit old and the Bent TAp with autoformer has been released. I did not own the previous version with the S&B trannies, but I did own a highly regarded S&B passive by K&K. I don't know if the difference is due to the difference in manufacturer, but I find the autoformer version of the TAP clearly superior to the S&B passive I previously owned. No leaness I can detect running my Music Reference RM9SE and incredible presentation of intonation by which I mean tracking changing levels of volume and and pitch which to me is critical to getting the musical message; that is, the new Bent Tap is very musically articulate. No loss of dynamics that I can detect compared with some highly regarded tube actives I have owned. With the right matching amp and source voltage, this passive is about as good as it gets; I think - worth an audition, especially if you own a tube amp with a 100kohm or higher input impedance and sensitivity half the output voltage of your source.
Are you using the Bent TAP with your Merlin BBAM upstream or downstream of TVC? If you're having good results, I assume that the BBAM must be upstream. The BBAM's 47K input impedance and capacitive load reportedly don't mate very well with a passive.
If I understand Bobby correctly, the BBAM is almost always preferred no matter what preamp you are using.