Also model 2's are about $15-20 average while model 1's can command prices upward from $60-80. I have heard rumors about a bug in the bios of the model 2 which causes Lunar 1, Dark Wizard, and probably a few others to sometimes freeze at certain points. Personally though I have not experienced such lock ups and I own Lunar 1 and Dark Wizard, and have played Lunar 1 to completion and Dark Wizard a good ways on a model 2 Sega cd.
Model 2s lock up, so do CDX's. Usually tapping them gently on the side will unlock them, but not always.