I was on the quest for organic mite killers for my chickens. I came across many possibilities. Elector PSP was by far the best. However, as anyone who has ever looked into it knows... It costs an arm AND a leg.
So I looked into neem oil.
The problem I came across was that there were two types of neem oil - cold pressed and Clarified Hydrophobic Neem Oil (CHENO). I researched and found out that they work in two different ways. Cold pressed damages the reproductive system of the mites, making them sterile. This does not work on the eggs. CHENO suffocates the mites, killing the eggs, nymphs, and adults (that's what I call a winner!).

The unfortunate thing that I realized was that CHENO had many warnings. (I.e. rinse any skin that comes in contact with it for 20 minutes under running water.)
This did raise a red flag, but I was still curious. After all, a can of Lysol says the same thing and my grandfather used to spray his feet with Lysol to kill any bacteria after working every day. (Poor life decision, I know. And probably TMI.)

I was planning to bathe the chickens in the stuff. I wanted them totally mite free. (Just so you all know, please don't feel like you have to do this. Lots of other people have had success with a little spritz of stuff.) Because of this, I wanted the product to be safe.

I ordered some CHENO to try on the run. It worked fabulously. I sprayed a 3in yellow jacket/wasp/bee creature as well as some other things, and some mites. I didn't hang around to watch the tiny mites, but it killed rolly pollies (pill bugs, I had to look that up) and the wasp. The rolly pollies reacted quickly. The wasp flew off, and then a few minutes later we saw it again. It was writhing on the ground as though it's nervous system had been effected. We didn't want it to be in pain so we dropped a rock on it.
Needless to say, the stuff is powerful. However, it IS NOT SAFE ON CHICKENS. Within 5 minutes of having some of the oil on my skin, my skin started to sting in that area. I had to scrub it under water with soap to get the stinging to stop. This was repeated a couple times even with the small amount of residue left over after I'd cleaned it on the outside of the container. I am very careful when I use it now.

My experience with pure neem oil:
It reduced the population of mites significantly. We power washed the coop, sprayed it with neem, and bathed the birds in the neem. I'd say the mite population was reduced by 75% over the course of 2wks. This, I'm sure, was also affected by the power washing. Nobody had any negative reactions to the neem oil. (Pure neem oil is actually used in skin care products!)

In the long run, we ended up buying Elector PSP second hand from a lady on Facebook. We were tired of fighting the mite battle once a week. We had a bunch of chickens (30) and my husband was slightly mite-ophobic so biosecurity was intense.

Thanks for reading! I hope this was educational.