Well, the general idea seems to be to treat MODY with small doses of sulfonylureas. I've heard some do well on small doses of insulin at meals. It may depend on the type of MODY you have:
MODY - It's Not Type 1 and Not Type 2, but Something New
If you don't have insulin resistance and your liver isn't dumping excessive amounts of glucose, I don't think the metformin could be helping that much. I think doctors say that just because it's not fully understood how/why it works. I ended up on metformin for 6 months despite really unpleasant side effects, but it never did anything for me.
