Type 2 diabetics on metformin live 15% longer than non-diabetics. This is remarkable considering how big a health disadvantage diabetes itself is.
Metformin seems to mimic fasting somehow, by interfering with mitochondrial function.
For more information I refer you to David Sinclair's numerous discussions on this topic. He takes 1 gram of metformin per day with his evening meal.
This is not medical advice.
At the begging I had nausea issues with it but eventually switch to longterm release and I’m the side effects went away unless I don’t eat.
It truly helps with controlling the appetite and brought my diabetes under control. I don’t feel any younger but I hope the studies/discussion mentioned are truly legit.
Metformin has numerous other effects: it reduces carbohydrate absorption in the gut, changes the gut microbiome, increases insulin sensitivity, reduces the liver's conversion of proteins to glucose, changes the way proteins accumulate in the brain (thereby making dementia less likely), etc.
When you're on metformin you can feel the physiological stress. It's like a mild attack on your whole body, a persistent slight discomfort. It's like a very mild poison.
You will lose your appetite and it will be hard to want to eat. You will tend to lose weight and eat just enough.
It can make you nauseous and you will probably find the bitter taste and fishy (amine) smell of the pills to be repulsive.
It is not an easy drug to take, and like you said, it may also affect male fertility.
But it is well-studied and safe, and offers various benefits.