Somebody mentioned it in a group and I googled. I thought it was worth a try as I have some.
Well, it may help if you're a diabetic rabbit or rat? (Those seem to be the scientific studies.)
In my personal opinion, an issue with non prescription drugs for diabetes is that if they have a medical effect then they need testing for efficacy and safety, and if they don't work, why bother? In particular, if they have similar ingredients/actions to prescription drugs then you need to know how much to safely take and what side effects to look out for.
An interesting warning from the FDA here
Beware of Illegally Marketed Diabetes Treatments | FDA
I realise you haven't bought your neem from a dodgy diabetes cure site, but the same principles of knowing what you are taking apply.
And in particular, knowing how much you are taking applies, as studies on neem leaves are not the same as neem oil.