For what it's worth, I, too, just put an 8120 into my 4Runner. I was tempted to go with the Kenwood cam, but the interface with the 8120 is just a simple composite connection, so there's no need at all to go with the Kenwood camera of something better suits your needs. I also looked at the Pioneer ND-BC20PA which mounts like the kenwood (traditional camera shape) but has a DSP that corrects for visual distortion and provides for distance guides. I think I'd pick that over the Kenwood, even though it's about $100 more on the open market. What I don't like about either of those models is that you still have something sticking out like an unnatural protuberance.
Ultimately, I went with the Boyo VTL300 backup camera. It's in the form of a license plate frame, and if you don't know what you're looking for, you wouldn't really notice it, especially the black version (it comes in chrome or black). I'm happy with the camera; it has good low light visibility and it's got a nice field of view. You do have to get used to the fish-eye distortion, however.
I'd rank the cameras thusly: 1. Boyo, 2. Pioneer, 3. Kenwood.