I am tempted by the Dexcom 5, but what put me off was the cost of having to replace sensors every 7 days. If, as you say, they last for a month, I might make the jump. I have no issue with calibrating twice a day, but I would likely make my treatment decisions based on the results of the CGM. Whether it is slightly out or not makes no odds if it can give a good approximation of trends. The suggestion that treatment decisions are not made from the Dexcom results seems a little ridiculous. If it cannot give you reasonable results when you calibrate twice a day, then it wouldn't be worth it. I sense this is a legal thing where they are just trying to cover themselves.
Did you go straight to Dexcom or via a distributor?