I tried both (DualHead2Go and USB adapter) and kept the USB adapter at the end.
- DualHead2Go: it creates a virtual display of the total resolution of your physical displays: 3840x1080 for 2 1920x1080 displays for examples.
* Pros: No lag.
* Cons: some windows are poised to be splitted between the 2 screens (login textfield, cmd + tab windows, etc.), you can't use fullscreen (for app or videos) anymore, in addition I had flickering issues with the device.
- USB adapter: it's like a secondary video output using the USB bandwidth.
* Pros: your display is recognized as a second display by Lion, less than half the price of the Dualhead2Go.
* Cons: some lag issue when a good portion of the screen is changed. You won't notice it when you do some word processing, internet or coding, but you definitely will when you drag a windows from a display to the other for example and you won't be able to play games or watch fullscreen video on this display.
If I could go back in time I wouldn't bother to connect 2 displays on a MBP and settle for 27" ACD instead. As I can't, I recommend the USB adapter over the DualHead2Go. Be sure to get one with the latest chip:
DL-195 and get the driver from the
displaylink website