I have one, that I was bought for a present when I had the Mk6, because some of the places where I used to park, people had a habit of parking a motor bike, or a scooter directly behind the rear doors where it couldn't be seen in the mirrors
It worked well in the Mk6, as it had a wooden bulkhead, and was a SWB, but not so well in the Mk7 with the steel bulkhead. I had to bring the camera sender unit as far forward as I could, almost to the rear of the SLD, to make it work, but as said, it's still a bit iffy in the mk7.
You may be OK, if you have line of sight, but I think that these are more suited to a car which is a shorter distance.