I know of several mirror couples that seem very happy.
Overall, I think mirror are good relations but can be a bit weird as I find the ISFp thinking I am a little careless or rushed.
No ISFp has ever said this to me but I suspect they are thinking: "calm down", "plan better", "you are late".
Also the slow methodical nature of the ISFp seems unnecessary. In my case with the ISFp its an issue of how to use Si.
How do you find Mirror Relations?