I have arctic frost and orange frost in the ground. One set is on its own rootstock, the other is grafted to trifloliate. Both were protected with Christmas lights and covers. This was their first winter. One set got down to at least 14 degrees and probably lower but I stopped looking after 3am. The lows for those three nights were 11, 3 and 5.
Here is Arctic frost (right) and Owari. Owari suffer the most damage. Where there were no Christmas lights, it died back. The Arctic frost had mild to moderate damage.
This is Orange frost and Xie Shan. No damage at all. The Xie Shan has fruit this year. The real surprise is the mango seedling to the very right, no damage. The Orange frost had fruit on it when purchased. I picked them in Sept. They were ok, not great and they had seeds.
The pair that were grafted also were no damage, but they are smaller and much better protected. These grafted ones are growing much slower. Part of the reason is that they're growing in native soil versus a garden soil for the others.
As of now, I don't have an opinion about Arctic or Orange frost. Other mandarins so far seem to be about as cold hardy. This last winter was fairly mild after those 3 days in Dec.