Nice review. I'm a fan of Surefire products too and have the X400U and X300U. I haven't tried the green laser version because I thought the price differential was not worth the brightness gain. The red laser is plenty bright for me even in daylight outdoors at a reasonable distance.
One thing I don't like about the design of the X400 is the battery compartment. IMO it pivots open in the wrong direction because when it's mounted to a picatinny rail, I can't swap out the 123A batteries without having to detach the entire unit. For the X300U that's not a problem but I'm worried that I have to re-zero my laser.
Other than that, it's typical Surefire quality. Bright, tough, and reliable.
Regards,
ED-209