I have been exclusively using virgin queens in my operation, since started producing them years ago. I like using virgins as opposed to cells so I can easily cull any inferior queens. Often you will find cells where the pupae died, or the queen has issues. (underdeveloped wings, one leg not working, etc) Allowing them to emerge in the incubator keeps inferior queens from wasting space in a mating nuc, or full sized colony. Many people have frustrations with introducing virgin queens. Sometimes it seems effortless, and other times they are annoyingly rejected. I've experienced almost perfect take, and have seen very poor. I noticed when holding queens in their nucs for instrumental insemination, that the queens appeared to be accepted and were fed in their cages. After the procedure, some were released and killed by the bees. This puzzled me. I realized that the colonies that were killing their queens had made queen cells. I slowly wisened up. I started making up nucs up a week in advance of adding virgin queens. I would move them to another yard, and put syrup on them to reduce stress. After 8-9 days I could cut any queen cells out and add a candy caged virgin. This allowed any young larve to age out past turning into a queen. Since they are in a hopelessly queenless state, there is no competition. The percentage of queens that are accepted is drastically increased. This is now my preferred method of virgin introduction, and queens that we instrumentally inseminated.