Backing up warning systems - which one?

[Decolliber]

My wife keeps backing up into things (like our truck, other cars, etc.). I would like to install a backing up warning system on her Forester. Here is one I found:
http://www.reversesafe.com
Has anyone tried this one? Its only $50.
Any others I should consider?
On a more philosophical note, why are women so prone to backing into things? My wife has had three "at fault" accidents in the past 10 years, and all three have been when she was backing up.

[bell]

i've been installing alot of these over the past year, i'll get details on the one i like the most tomorrow, i forget the brand as we get them in plain white boxes in bulk.
pretty slick though, it has 4 sensors which get installed in the bumper, it's pretty much identical to the ones that come stock on the new caddy's and they come with paintable mounting rings.