Medicare Supplement "Core" vs. "One" Plan
Oversight for Medicare Supplement plans comes from the state, not the federal government. The states mandate the coverage that must be provided. Most states have a series of Medicare Supplement plans that are designated by a letter of the alphabet, each different from the other. As one of three "exception" states, Massachusetts has only two plans: The Medicare Supplement "Core" plan and the Medicare Supplement "One" plan.
Most Massachusetts carriers have branded their respective offerings by using the "Core" or "One" names, but some use their own brand. You can tell which is which regardless how the product is named by the premium. "Core" plans are exactly what the name implies; they are stripped down versions where deductibles and copayments may apply. In 2016, for example there is an $1288 hospital deductible when someone is hospitalized. This applies every "benefit period", which is an every 60 day period after someone has been released from the hospital. That means that the deductible can be owed multiple times a year. The hospital deductible is changed annually and is associated with Part A of Medicare. A much smaller Part B (doctors) deductible and copayments for some services also applies to the "Core" plan. Most of the time the "Core" plans do not cover you outside of the country.
The "One" plan is always more expensive. It covers most copays, all Medicare deductibles and it covers beneficiaries world-wide for emergent or urgent care. All Medicare approved services are covered so once the premium is paid there are, usually, no further charges for hospital and doctor services.
As mentioned all carriers are mandated to offer the same benefits and they all have the same doctors and hospitals in their networks. To differentiate, look at the premiums and see if they offer any extra benefits. If you used a certain health carrier during your working career but they offer a more expensive Medicare Supplement plan, it makes good sense to consider other health plan carriers once you elect Medicare. The basic benefits are mandated by the state, so why pay more than necessary?