With any drug you should always be careful and seek a doctor's advice on whether it's right for you. What excites me about metformin is it's on the path to become the first medication licensed for treating aging itself and is generally well tolerated by most people - and it's cheap too.
When the current study concludes I really hope it starts being prescribed en masse for aging and I also hope the attention on metformin inspires further work in the field of interventive biogerontology.