I remember reading about pollinator flies in one of my plant-breeding books, although I don’t remember which one.
According to what I remember from the book, one of the big advantages of using blue bottle flies is when you’re trying to keep varieties isolated. You can grow the different plants in mesh (or netted) cages, and stick some fly larvae in each cage. They’ll mature a short time later and start pollinating, without any chance of them having picked up outside pollen.
The life cycle of bees just doesn’t allow for that.
I haven’t tested this myself, but it’s on my “someday” list. There are some plants it’s hard for me to keep isolated.
If you go to the article link I posted, the carrot guy has those mesh cages .... it’s a pretty cool way to do the pollination .... he loves the flies!