 but they offer a far narrower range of doctors and hospitals. Even still, once seniors become eligible for Medicare, over half of them turn to a Medicare Advantage plan. Tricia Newman is with KFF, a health policy think tank. The plans are marketing aggressively and offer extra benefits. Newman says people might pick the lower-cost Medicare Advantage when they're healthy, but if they later get very sick, they can find themselves trapped in a network with fewer options and higher out-of-pocket costs.