When I was first diagnosed I was given metformin along with stronger stuff, with diet, exercise, and maybe some good luck I've managed to get rid of the stronger stuff and just stayed on metformin for years now.

No effect on weight as such. With the metformin, diet, and exercise my A1C has generally stayed below 5.7 so I've experimented with cutting the dosage, and have occasionally forgotten to take a dose, so I can report it seems to reduce blood glucose readings by ten points or so, and if I had to stop taking it I could probably still keep my A1C close to where it is - but couldn't cheat on the diet as often, LOL. Missing one dose generally has little or no effect.

The only issue is that it sometimes keeps you hopping towards the toilet more often than is convenient but even long before I was diagnosed with diabetes I sometimes had bits of such "irritable bowel" as well so I don't know how much to blame the met.