The problem is that because your groups are so small (essentially its just you when you pay the bill), you have no leverage to get lower prices from the providers. You have to pay the top rate bill. Insurance companies can threaten the providers and get them to reduce the bills. Ultimately, the best system is the English NHS and similar. Everyone pays in through taxes, and every one is treated when they get sick. ZERO stress about whether you have the money to pay, whether they accept your insurance, if you are out of coverage area and so on. The savings in billing and accountancy alone are huge. And the removal of the profit incentive has huge dividends for society. In America, they will sell you anything to get another paying customer in the door. If you are in a car accident, you will "see" 5 consultants before you even wake up. Each of whom did absolutely nothing but throws a bill at you nonetheless. Where there is money to be made, there will be scams.
RE: A decentralized solidary group as an alternative to health insurances. Artabana.