In Wii-U mode, the Mayflash 4 port will be console accurate. In PC mode, it will be quite accurate (as long as you are using a genuine Nintendo GameCube controller). Dolphin still has some controller emulation issues to work out, but they are not caused by the adapter. See Issue 960, Issue 6780 for two examples.
In Wii-U mode, the answers to your questions are: 1) No 2) Yes
In PC mode, the answers are 1) More than in Wii-U mode 2) No
In PC mode, the Mayflash will have around the same latency as the Xbox 360 controller.
In Wii-U mode, the answers to your questions are: 1) No 2) Yes
In PC mode, the answers are 1) More than in Wii-U mode 2) No
In PC mode, the Mayflash will have around the same latency as the Xbox 360 controller.