I just had a chance to test the XTR-690 after Mike fixed mine back. A few impressions that I got:
(1) The new lens is a big improvement. I'm very impressed by the visibility now.
(2) POP mode seems to really really increase amount of falsing. Annoyingly so, at times.
(3) Ka band sensitivity is simply impressive on the XTR-690
I've also tested against a Cobra XRS-9300 11-band.
When within like 5 feet of the Cobra, the XTR-690 falses on Ka band no matter what filtering mode.
At a more reasonable car's length, the XTR-690 is a LOT more resilient to Cobra falsing than my 1793SE. My 1793SE still picks up like Ka 4, while the XTR-690 picks up basically nothing in all 3 filtering modes.
The detector overall, when POP is OFF, is a lot quieter than the previous generation.