will this work with a custom flash? did you ever use it? any helpful info would be appreciated

 

This will work with a custom flash. All this unit does is cut fuel/spark so that your RPM's are maintained at a desired level. It serves the same purpose as the stutterbox's on the 2005 Evo's, so that you can launch at whatever RPM you wish. I myself never installed it but according to other EvoM members this unit is bad ***.