After almost 3 months I am very satisfied with my purchase. I will tell you though I use SmartSDR 99.9% of the time to control my 6400M instead of the Maestro that is connected to the front of the unit. When I upgrade to a 6600 it will be sans the Maestro. I also use the FlexControl in RTTY contests which are my fave contests (no sprints, I hate sprints).
Here’s a pic of my 6400M with my FlexControl: