I Find with big swings my sensors go quicker. My longest sensors are when my BG is flatlined in the 80-120 range. The swings also get the 3Qs more often. I try and calibrate through the questionmarks. As long as I get at least 7 days out of a sensor I am happy. Most of mine last 3 plus weeks though.
Yep, I think using arms is the key. No appreciable longevity with any other sites.