Some gardeners question the usefulness of neem insecticide.

They sprayed neem oil, and did not see an immediate effect. They probably did not understand how neem oil affects insects.

Neem oil does work, but the way it works is different from other insecticides. Neem is not an instant, knock down, kill everything pesticide.
Read further at the attached link below.

Here is a link that might be useful: How Does Neem Insecticide Work?

The directions said use a wetting agent????

I know there's a neem oil that's advertised as a leaf glosser. I'm not sure if it's the same as the 70% neem oil extract that is sold as a pesticide/fungicide. None of the different brands of nem oil as a pesticide that I've bought over the years told me to use a wetting agent/surfactant or anything other than water.

You've gotten good advice from NECM.

In my opinion, neem oil is a rather pricy fix for Aphids. Blast of plain water every 3 days or so is actually quite effective. Insecticidal soap would be my next choice, then neem. The key is diligence. Aphids reproduce at such rapid rates that you may not notice a difference for a couple weeks until you bring the populations down to manageable status.

Kevin