@Alan I am not very picky about the neem oil. I have been using a commercial homeowner brand that I get at Lowes (Garden Safe Neem Oil Extract). At some point I would like to try some of the other “better” neems, but this seems to work.
My formula is per gallon: 2T neem (per label instructions), 1T Dr Bronners, and I also add 1T potassium bicarbonate to help with mold (baking soda would work but my GH soil is already high in sodium so I use the potassium version).
I often in winter need to heat the neem to get it liquid, and use hot water for the first portion of water to get the neem mixed in. Then use cool water for the rest.
I apply it to any/all green plants in the GH (anything the whiteflies might be eating). Citrus and sometimes, tomato, peppers, eggplant, greens depending on what’s growing.
The neem product is labeled for insect use (and oil sprays are used on aphid and whitefly). Can’t say about the others.