I opted for the top-rated (and pricey) Brandmotion RADAR-based unit, and had it installed by an authorized installation shop.
When I saw the very detailed (and somewhat complex) installation instructions, I decided it wasn't something I wanted to tackle myself. (The older I get, the more dollar value I attribute to what I call "The Hassle Factor".) It requires using a protractor to bend mounting bracket angles and aim the RADAR emitter/sensors. (I may be an engineer, but I ain't got the patience for that!) It's mounted entirely behind the rear bumper fascia, with no exposed emitters. (The RADAR passes right through the plastic.)
I'm extremely pleased at how well it functions. It was about a grand, all-in.
I know this doesn't answer your specific question, but I can say that you'll need to be prepared to do some very careful and precise work, in order to get good results.