I too have a Dingoo. I've had it for about a month and my Wiz for about 3 weeks. Let me just say first that you will find yourself blown away by the Wiz, moreso than the Dingoo. I initially liked the Dingoo more when I first got the two, because it could do more. At the Wiz's launch there wasn't much for it. But now the Wiz is by far more impressive. As for your specific questions:
1. As for Starfox, it handles it better than the Dingoo (it just crashed on my Dingoo without loading). On the Wiz, the game loads fine, and begins but as soon as you get to the opening cinematic (where your ship travels through the tunnel) the emulator experiences significant lag, and finally freezes the game. The emulator itself is still running fine, and the menu is still accessable, but the game freezes.
2. No problems that I've noticed yet. In some emulators and games that utilize the touchscreen, it appears there is some difficulty in keeping the touchscreen accurate. For example, in SCUMM, if I attempt to touch the top left corner of the screen, the mouse cursor appears directly under my stylus. However, when I attempt to touch the bottom right corner of the screen, there is a noticeable gap between the point where my stylus is touching the screen, and the point where the mouse cursor rests.
I wouldn't worry too much about all of that though, as the particular build of SCUMM I'm using is a VERY early build and it has very few (if any) Wiz optimizations. It should hopefully be fixed in an update sometime.