I use a Dexcom G5 and find it invaluable. Before getting one I was testing on average 7 times a day, and was still missing most of the night and unexpected post-prandial highs.
If you only want to use one occasionally, or cost is a concern, and don't need the low blood sugar alarm, you could look into the flash blood glucose meter, FreeStyle Libre. The sensor is smaller because it doesn't have a transmitter, and you hold the reader over the sensor to catch up on what's happened since your last reading.
Otherwise Dexcom is considered one of the best CGMs. I think it's worth the cost, I pay for it 100% myself (which comes to ~$4,000 US/year).