Hi Stewart. I started on the Tandem and Dexcom last fall, after meeting with a new endocrinologist. I had been on a Medtronic pump for two decades, but I hated (and did not at all trust) the Medtronic CGM. It was constantly wrong, and there was no way I was going to update to a closed-loop system with that, so I completely understand your fears.
I have my issues with Tandem and Dexcom - I wanted them to be the magic sauce everyone that was on it claimed they were, but they are not magic. And after years of managing my own diabetes, I know my body better than the algorithm does.
That said, it is still miles better than before I had them. A few of the Dexcom sensors had trouble getting started and I had to use fingersticks to calibrate them, but once I have about three calibrations in, they were spot on. The first 6 hours or so on a new sensor I watch carefully, then I have 10 days of not worrying. It’s never caused me to go high or low with it’s adjustments.
That said, you can toggle the Control IQ on and off at will. My overnight numbers were completely irrational. For no reason, I would wake up super high, or super low. It wasn’t connected to eating or exercise or stress, and it wasn’t predictable so I had no ability to manage it. That was the main reason my Dr wanted me on the tslim, and it has totally worked. My night numbers are amazing. I wake up nearly every morning around 105, and the overnight line is usually flat (from about 2am on, I am hovering between 100 and 130).
I do sometimes turn off the Control IQ during the day, though. I can predict what my BG will be if I am in my routine, so it is a little like just taking shots. I bolus when I eat, and if my Dexcom warns me I am high or low, or I check and see it is trending one way or another, I can adjust before I feel it.
Also, it doesn’t make huge changes. Like, if you are really high, it isn’t going to bolus a ton of insulin all at once for you. It will give you a little and increase your basal and see where it goes before giving you more. The Dexcom allows you to see what is happening and choose to adjust yourself (or test, until you are comfortable trusting it).
It is expensive if your insurance doesn’t cover 100%, so take that into account. It doesn’t make the diabetes go away, and I still can’t get things perfect. It isn’t a pancreas. But it definitely helps, gives me more information, and seems pretty trustworthy.