The Romtec Colorvision seems to be missing from the Video game handheld rarity guide.

In regards to rarity Id place it behind the Adenture Vision and the Epoch game pocket computer IMHO.

More info on it can be found here at the handheldmuseum: Romtec Colorvision system

and

The www.HandheldMuseum.com Forum :: View topic - WHAT IS THE ROMTEC COLORVISION WORTH?