How applications behave with Matrox Dualhead2go?
I have this product.  All your concerns are valid.  Modal dialogs and prompts are split by the program's bezel.  The dock can be positioned across only one monitor, but that is the only configuration option.  Fullscreen video on one monitor is not possible.  Fullscreen apps span both screens, which doesn't work well. Calendar is OK.  Mail is impossible, especially when composing a message.  It is easy to maximize to just one window using built in hotkeys.  However "true" fullscreen is usually complicated by monitor bezels.