PCOS is basically a fubarred hormone system. Insulin is a hormone, so even if your insulin and glucose are working together in harmony (Everybody sing Ebony and Ivory now), that whole hormonal balance is going to be changed when you introduce Met. That could be a good thing or an unnecessary thing. (However, it does help adjust androgens, which are normally off with PCOS).
I took it when I felt like I had to. I was losing hair where I shouldn't, growing it where I shouldn't, gaining lots of weight, in pain from ovarian cysts, and acne was going wild. Not a pretty picture. Met made me sick and I didn't stick with it for too long, but it was long enough to knock off a few pounds and get me and my symptoms back on track.
Personally, I would only get back on Met if I felt I had no other choice. I'm afraid of the side effects, and balancing them out with what I need to correct, I'm choosing to not do it for a while longer. If I can't take care of things holistically, I'll give it another shot, maybe. If I wanted to conceive, or if I was dealing with multiple problems like before, I would definitely give it another try because I'd rather risk side effects than live like I did before.
I know you have tough decisions, and I hate it that you have to make them.