Hey sorry for the late response. My mother is the medical billing and insurance specialist for a private religious organization. She moves all the nuns from their private insurance to Medicare as they become old enough to qualify.

What I've constantly heard from her is that the standard benefits are enough to cover everything but the private addons advertise they can make it cheaper. But as soon as you sign up, Medicare stops covering parts that private addons do (because the private insurance is now getting money from Medicare). This forces a lock in where you can't really go back.

Also from conferences she has attended, there are experts in the field predicting these private insurances are going to bleed Medicare dry from increased costs. What's happening is they keep adding these benefits that only some of their customers use (like silver sneakers membership?) then telling Medicare their operating costs have gone up and they need more money.