CMS is the abbreviation for the federal government agency, Centers for Medicare and Medicaid Services, that oversees Medicare. This federal agency is responsible for publications, email messages and oversight of Medicare insurance policies and Medicare medical providers.
Over the years, many Medicare advisors have written extensively about the "disadvantage" of Medicare Advantage insurance plans. I have pointed to some of those articles on this blog and written about the push, particularly in the last 4 years, by the federal government to get Medicare eligible participants to enroll in Medicare Advantage insurance plans. It makes no sense, because these plans do not reduce the tax payer burden for the cost of Medicare. It would appear it is CMS's way to privatize Medicare and thereby get millions of dollars in campaign donations for the pushers.
A non-profit organization, Center for Medicare Advocacy (CMA), has been trying to hold the federal government accountable and expose it. There are a huge number of pitfalls associated with Medicare Advantage plans. Most of these insurance plans, to put it impolitely, suck. Kaiser Permanente is about the only one worth considering but it is not available in many areas.
Here is a link to a recent "alert" document by CMA:
https://drive.google.com/file/d/1dyJuWaxDOz9DcCKyiuPAT2-8mzYJJ7_K/view?usp=sharing
To access the file, at least when I tested it, I had to download it.
The bottom line - which I feel is sad - I DO NOT recommend you rely on federal government literature as your only source of education about your Medicare choices.
There are several non-profit groups like CMA and Medicare Rights Center (1-800-333-4114) who offer a balanced approach to Medicare information and in MRC's case, provide Medicare counseling. The state health insurance assistance department for your state (which is found at www.shiptacenter.org) also typically provide honest assessments as that is not where insurance industry lobbyists spend a lot of time. The library might also be a good source of Medicare information. What is not a good source of information? Insurance agents, and, unfortunately, the federal government because they are both biased.