I had an original 8500 (not x50) and it served me well I also sent it in to get upgraded for my other car, loved the unit.
In April decided to upgrade to the 9500i, so I had one of the first models and it had a few issues with ramp up and k sensitivity. True lock was always fine for me because I only need to lock out 2 places for my ride to work and KA is only used in my town.
I just returned my 9500i for a new one (herd about the improvements) and the k band seems to be much improved and ramp up seems to be a bit better (Not Perfect) KA was always good.
I love it. No false alerts and when it goes off I know to slow down on the 1st beep. It has saved me a few times...
FYI, I spoke to Escort about auto mode. Auto mode decreases sensitivity at 15mph and under.