I have had very good experience of the standard type 123 Danny. I fitted one fourteen years ago, selected curve 7 as recommended for a TR engine in fairly standard tune, and found that the advance at various engine speeds exactly matched the predicted figures. On test the car pulled away with no pinking or hesitation if the throttle was floored at 30mph in top and pick up was clean throughout the rev range. I found low speed running to be smoother also. I have had not a moment's trouble with the 123 although of course I do carry the original Lucas distributor and leads assembly on board just in case. (A few years ago I lent it to a Dutch entrant on the Border Raiders and it did the whole event and the journey back to Holland without a problem).
The 123 replaced a Lumenition Optronic system I had run for over 20 years but on which the power pack had failed. I knew that the original Lucas distributor was worn, with stretched balance weight springs since the advance could be variable. Of course the Lumenition system catered for distributor shaft wear as it dispensed with the conventional points but I was still left with the worn mechanical advance. The 123 cost £185 in 2007 which was comparable with the cost of a replacement Lumenition or a full distributor rebuild so for me the fully electronic 123 solution was a no brainer. The 123 distributor was originally recommended to me by Jon Ranwell, a C.T. member at the time, who had had very good results with one on his Spitfire Mk III.
Tim