I think the 4mm needles suck.
They are promoting them because of the overly-cautions worry that people are accidentally doing IM injections with the longer ones. So they just want to push everyone into using shorter needles.
It’s akin to getting a 5.5 A1C and an endo saying it is too low.
The deeper depth will give faster absorption.
When they do those studies, they are not necessarily doing them on the elite diabetic community. So take that into consideration when you see stuff like that. Are they saying a person in the 5’s or 6’s didn’t have an increase in their A1C? Or are they saying a person in the 9’s, 10’s, or 11’s, didn’t have an increase?
You never know who was included in the study, so always apply what works for you. If you try 4mm’s and it does not work well for you, that is all that matters.
I will never go back to 4mm. They were horrible for me.