I switched from DexCom to MM because I got peeved at their upgrade policy for the Seven Plus (when they were upgrading people) - charging more to the people who’d already spent the most and been on their system the longest. This also motivated me after years of MDI to try a pump, and I’m loving the results.
When I first got it I was experiencing some serious accuracy and other problems with the MM unit, but it turned out I just had a defective transmitter and they replaced it without complaint.
Even now, while vastly improved, it’s not always as accurate as I would like, esp. on the first and last day of use, but the DexCom was not always all that accurate either, I would experience it being 100 points off at least semi-regularly. (I think it may have been better than the MM but hard to say without comparing numbers - when I first got on the MM unit I knew it was way off, comparatively, but that was before the transmitter replacement, which has vastly improved my results.)
One thing I’ll say - the sensor wire and insertion needle on the DexCom are smaller, so I get more bleeders now, and not having to use tape over the sensor/transmitter on the DexCom is a lot more convenient in the shower. But I wouldn’t go back - Medtronic is much better to deal with vis-a-vis insurance since they’re directly contracted with some insurers, their customer service is outstanding, and I simply do not want to carry multiple devices.