The R20X is an increasingly popular hybrid dash cam and backup camera combo as it's a very cost effective way to kill two birds with one stone. The dash cam has excellent video quality at 2K front and 1080P rear (Sample video here). This also translates to a very high resolution backup camera, since most factory and aftermarket backup cameras are only 480P (VGA), this rear camera is noticeably sharper.
Another reason these cameras are so popular is that they are fairly discreet. If you don't want to add a screen in your car or change out the factory radio, this is probably the cleanest way to go about adding a rearview camera. Perhaps the trade off is that the viewing angle is a bit narrower since this camera is meant to work also as a dash cam. Backup cameras don't typically need to see very far as they are to warn the driver of a closer obstacle, but dash cams need to see further down the road (more than a car length away) to provide useful information for insurance purposes. A dash cam that's pointed at the ground will not be much good in the event of a rear ender.
For this Sonata we were able to mount the rearview camera dead center since it does not have a trunk release button. It was also small enough that we could mount it inwards where it shouldn't get bumped by anything since it sits fully under the chrome trim piece.