Hi Nicole,
I currently have MM pump and Dexcom Gen4 CGMS. I've used MM pump for 15+ years, Dexcom CGMS for 2 years. Prior to Dexcom, I used MM CGMS for 2.5 years.
I have much better results with Dexcom CGMS, and I find it more convenient for my lifestyle. I prefer having it as a separate device than the pump, because I can set it on the table/desk and see it more frequently and make adjustments/corrections sooner. At nighttime, I often missed MM CGMS alarms, with the pump under the covers. With Dexcom, I keep the receiver under my pillow, and hear them every time.
In another post, I referred to the MM CGMS as 'high-maintenance' compared to Dexcom.
With MM, I used each sensor 6-7 days, with a restart at day 3 and 6, and battery recharge/new sensor on day 7. I had to be careful with when to enter calibrations, and often calibrations did NOT seem to get the CGMS back on track. Trends were often inaccurate - it might show going up slightly, I would check BG, and find it 100-150 pts higher. I had many lost sensors, CAL errors, etc. I actually found TuD after many frustrations with MM CGMS, and was searching for help !
With Dexcom, the calibrations can be done at my convenience, and each sensor lasts 10-14 days, and sometimes more. Most BG readings are within 5-20 pts, and when occasionally off by more, I enter a calibration and Dexcom usually adjusts accordingly, and much quicker than MM did.
After switching to Dexcom, and making some changes in diet, I was able to reduce my A1C from 6's to 5's. For me, Dexcom showed less lag-time from BG rise after eating, so it helped me identify better food choices, and better timing for my insulin.
