^Alex, I saw that thread and we've done about 10 installs with the mirror installation already so I know all about it. The mirror setup is good if you don't mind spending the money and personally I don't care for it.
The end question is where are you going to mount the main unit since even with mirror display you need to put the main unit somewhere. I don't want it in the headrest as previously mentioned because it blocks Laser. Plus I do not want to destroy my headrest. There are plenty of ways to conceal both units. For myself this setup works really well and super clean. Nothing mounted on the windshield!
As for the remote display in the ashtray, novel idea if you want to hide it and it's easy to do but next time you are going 100+mph, try look down at your feet or ashtray for more than a second ~ VERY SCARY right? I think that is a horrible place for something you need to glance at often and it must be in your "line of sight".