We get this question daily and both these detectors the Escort 8500x50 and the Beltronics RX65 share the same antenna and performance is almost identical. Escort & Beltronics merged quite some time ago and their newer detectors share the same technology but there are usually slight feature differences between the models.
When coming to these two models we like the Beltronics RX65 better because you get more detector for the same price. The Beltronics RX65 radar detector adds Voice Alerts and also supports the international KU Band. Voice alerts in my opinion make a detector much less annoying when an alert goes off since it will beep to get your attention and then tell you in a voice what band it is picking up. I like this much better than just a constant beeping tone.
As far as the KU Band is concerned there is no KU Band radar guns used in the US or Canada but if you travel internationally its worth having. When both detectors are priced the same it only makes sense to get the Beltronics RX65 in our opinion.