They often offer benefits that are very tempting, but if you run into a serious situation involving, say, home care, and need an extension of hours per day or toatl weeks, the decision on the appeal is made by an insurance company concerned with its bottom line.
This information comes from an independent patient advocate who deals daily with complex situations and knows the systems thoroughly.
One should also note the lawsuits that developed when the Adams administration in NYC decided it wanted to switch all its retirees from traditional Medicare to an "Advantage plan."