2 X CR123's will need a silicon diode to drop voltage. The FlexDrive (or Micro BoostDrive) takes 5.5 volts max input voltage...I am using a cree host designed for a 18650 and putting two CR123's instead. I was going to use the 405 lens because I have an extra but I may look into the 445.
Below is a pic of the host I am going to use I have an extra and a quick vid of my maglight laser vs my cree laser
I was worried about the flex overheating I have an extra do think it would be a better idea?