This is an old thread, but anyway...
My MG90S seems to work otherwise well, but if I do write(0), it goes to 0 degree and pushes over limit, slowly and vibrating. It obviously slips some gear meanwhile, because next write(180) turns it 180 degrees from the position where it twisted itself while performing the write(0) over limit. So if I use the range 1 - 180, I'll be fine.
Doing write(190) doesn't do the same thing. It seems to stop at the same point as write(180) and doesn't vibrate. So one has to kind of test each servo, just in case, and only use the values that make the servo behave ok.
Another good thing to test is measuring the angles, if precise angles are important. When I make my servo sweep from 1 to 180, it sweeps some 190 degrees.