If you have to use something while using insulin then Metformin would be a slightly better choice.
But IMO and
@luki7788 can chime in here as well. In most cases when guys are needing meds on a growth phase while using insulin there should be no need for this if your diet and cardio are dialed in. And are supplementing GDA’s IF needed worse case.
Better said- your using insulin, the number one medication indicated for high BG. Why in the world would you need to stack metformin on-top of it. Most shouldn’t.
When I’m using heavier insulin in a progressive phase my A1C drops because my blood sugar stays lower overall.