I've been very happy with my Valentine One, but I got it before they added POP protection. Since then they've had trouble with the RD "Junking" real alerts. They are still working on it as users are complaining like crazy. I've resisted getting mine upgraded for just this reason. With that said, Valentine will upgrade the RD free for one year after purchase if they come up with a revision change. Even after that it's only been $50 to $75.
If you really want to research the difference between the two RD, I'd suggest http://www.radardetector.net/ as there's a ton of good information there.