People who are not banded might nonetheless have close friends or family whom they have watched go through this, and are eminently qualified to comment.
It works for many, but just as many have serious side effects (nutrient malabsoprtion, excessive vomiting, band slippage, perforation, embolus, etc.). I knwo a husband and wife who had the surgery done together, and though they initially lsot a great deal of weight, their excess flab had to be surgically removed months after the initial surgery, and then they gained virtually all the weight back.
As to the diabetes “cure” well I would not believe that in a “few days” a condition which requires a lot of medication is completely reversed overnight. Yes, weight loss will absolutely help a diabetic, but it takes weeks, not days to see that change. Any change is probably because the person is eating far fewer carbohydrates and calories. Without a lap band, the same thing will happen if a healthy low-carb and good carb diet is followed.