ours worked - just - with a camper van - you had to be v careful and the sensors at the time showed us the distance as well as using audible warning, which helped, you just had to remember to 'add on' adjustment for rack when it was on - folded, and on loaded
we had it fitted privatelyby a Lancaster firm, can't remember the make, sorry, but it was possible to get sensors capable of of greater distances that the usual factory fitted options.