What's wrong with the 600Pro? 

It and the Big John Computrol are the only "advanced" planter monitor/controllers I have used, so i don't really have anything to compare with, but I've had no problem with the 600 other then it being somewhat more complicated to operate then what I would consider ideal.  It has a lot of capability, but I would be better off with less capability and an interface that anyone could operate.  Other then complexity, I have had no problem with it.