That is not true. Federal employees only get Part A and have a right to reject Part B and keep their Federal Employees Health Benefits which then pays what Medicare would pay doctors.
Sure you can reject Part B, but the rest is still in fact the truth. You MUST use medicare as primary, and cannot go to a doc or hosp. that does not take it. If your doctor stops taking, you must change doctors. The retirement insurance pkg. is seldom of any use.
Fed. employees I have no idea about, as that includes Congress, whether or not it should.