I say mite free. Since the treatment in late December I have checked the board under the OMF for debris and have found little or no mite drop in the weeks since. Not a perfectly scientific approach I admit, more empirical if you will, but it gives me confidence that the treatment was good.
I also plan to open the hives up this weekend to do a proper early spring inspection and also to remove any old frames. I left several supers on the hives over the winter as they contained some heather honey I couldn't extract. I will be checking the brood (quality and location) and will look to remove any empty supers, especially if there are any signs of wax moth. I hope to reduce the empty space in the hive.
The inspection will also give me a chance to see if I need to embark on any spring feeding.
In the meantime here are some photos and videos I took of the hives. I love listening to that buzz!