I used Apivar in my hives this fall, and it worked very well. Knocked the mites quick and hard, and easy on the bees, as far as I can tell to this point.
I went into one of my beeyards a couple of weeks after the treatment and the hives were dusting the mites out the enterence of the hive. I was running between 2-5% fall infestation, with a few yards around 10%.