Parking Sensors - Ultrasonic Vs Electromagnetic

[Catweazle]

As I just can't seem to judge the distance of the car behind when parking due to the RAVs higher level, I've been thinking about installing some aftermarket parking sensors.

As the electromagnetic ones don't require any drilling of the bumper they seem the preferred option but do they have a downside as most aftermarket ones seem to be ultrasonic? Is there a catch?

[bothwell_buyer]

you can buy simple (strong) horseshoe magnets which when attached to the rear bumper will actually attract the parked car onto your own - hence they have driven into the back of your car. An insurance claim ensues and you get £2000 for whiplash and other damages. Its enough to employ a man with a red flag to help you when parking. You just have to repeat the exercise every 2 months.

[Catweazle]

you can buy simple (strong) horseshoe magnets which when attached to the rear bumper will actually attract the parked car onto your own - hence they have driven into the back of your car. An insurance claim ensues and you get £2000 for whiplash and other damages. Its enough to employ a man with a red flag to help you when parking. You just have to repeat the exercise every 2 months.

Hmmm, thanks but maybe I'll pass on that idea. Has anyone actually fitted the electromagnetic type of parking sensors to a 4.2 RAV?