Adoannie, who told you that about the prompt payment? That's interesting.
Also, not necessarily true for all plans. In our state, there are areas that will not accept certain Medicare Advantage plans, although they take others and definitely accept Medicare and a supplement. With the crossover between Medicare and supplements, often a provider files one electronic claim and payment comes both from Medicare and the supplement, IF the provider accepts assignment.
Medicare Advantage plans are a reincarnation of Medicare + Choice plans that were started years ago, so that seniors would have "choice." Most of those plans dropped out, some of then abruptly, so then this "Medicare Advantage" was developed, with the subsidy. Plans have yearly contracts, so change every year and can drop or add plans. This year, where I live, 4 plans are not available next year, which means those people in those plans must find another plan, IF they read their mail and find out what's going on. Otherwise they will probably end up in traditional Medicare without the protections of an advantage plan or a supplement. If their Medicare advantage plan also had drug coverage, they could lose that if they don't pay attention.
My theory is that as people age, they don't necessarily want to review their medical plans every year. They want to do other things in retirement. But, maybe I'm just lazy.