Agreed. And if one does not sign up immediately there may be an additional cost after.
My Medigap policy is an "F' designation, not offered anymore, and I have no intention of changing it.
But for Part D (drug) coverage, I check every year on the Medicare site - there is a good tool to compare costs between different drug plans. Every year one should use the Medicare tool to compare pricing on drug plans. One year I was distracted and ended up paying $900 more than I would have with another plan - all because that plan had Tier 1, 2 drugs subject to deductible before lower pricing. All the other plans did not do that! I had to pay full retail until I reached a deductible of $480. So people with original Medicare and a Medigap plan, that can stay the same, but you do need to check Part D coverage each year. But it is easy to do and easy to switch Part D plans. You input the drugs and it tells you how much each plan will cost you for the year. All these insurance plans do not give one choice but confusion. We all need good coverage at reasonable cost, and not a whole bunch of plans we have to spend time figuring out.