@Nicole4 gives great feedback on her CGM and pump. I would entirely agree with her on the CGM. We also find the Dexcom extremely accurate although often times we only bother with one calibration per day and no other confirmation fingersticks. Dexcom does say to provide 2 calibrations (per day) for the G5 - but with just the one we find it only off by a couple points IF we pick a good time to calibrate which is straight and level and in good range. Never calibrate when really high or low - that is just messing with the system. Similar to @Nicole4 we are also waiting for the pump enhancements that will integrate the Dexcom and ultimately provide the closed loop.
We are not willing to get a closed loop with somebody different if we don't trust their sensor as the sensor drives the entire system.
@jteacher You mentioned your son just turned 7. That would just put him just out of the "under 7" warning from Medtronic. However AFAIK it is only FDA approved for ages 14 and older. Obviously Docs do "off-label" things but you would have to decide if you were comfortable with that.
@jteacher - Rather than jumping right to a pump to try and control your son's swings, I suggest you speak with other T1 parents of small children. A diabetic child is VERY much different from older people. What works for young adults, middle aged adults and older adults WILL NOT work the same for small children. A pump is not necessarily going to fix that for you.
"WARNING: Medtronic performed an evaluation of the MiniMed 670G system and determined that it may not be safe for use in children under the age of 7 because of the way that the system is designed and the daily insulin requirements. Therefore this device should not be used in anyone under the age of 7 years old. This device should also not be used in patients who require less than a total daily insulin dose of 8 units per day because the device requires a minimum of 8 units per day to operate safely."