Anyone have any experience with the Doppler unit on this website?:

http://www.sensetech.com/guardianalert.htm

Thanks for finding this. I have been waiting on a hitch connect one from Audiovox since last July (ash300). Bought this one based on your post.
Pros: Works well at all angles, easy to hook up, price ok ($299), no drilling, and spare doesn't interfere.
Cons: Cheap plastic materials, had to buy a lock for the hitch (should come with one), had to re-drill holes to fit within hitch otherwise it sticks out a few inches, and once you stop it doesn't make sound again until your speed builds therefore not great for parallel parking.