Sorry to be fickle with my response but when researching a CGM you need to think first about why you want it.
Is it to look back at what your readings were when you were not pricking your finger, you could go for a Libre (not continuous because unless you attach a Bluetooth transmitter it only tells you the results when you as it)? Is it to warn you when your BG is too high or too low? These are more expensive.
Is it to review trends to understand how different foods, exercise, etc, impact your BG?
Is it to replace finger pricks? If this is the case, bear in mind there is a 15 minute delay compared to finger pricks and the DVLA do not accept CGM readings when driving.
What do you mean by "simplest"?
Simplest to set up? Simplest to read? Simplest to understand what to do with the results they give? ..
Are you expecting to have to pay for this or can you get it on the NHS/insurance?
They are not cheap and they are an ongoing expense as the sensors only last a couple of weeks.
Do you intend to wear them at all times?
Once they have been activated you cannot take it out and then put it back in.
You may find it useful to get a trial.
My Diabetes Nurse arranged a trial of Libre and DexCom and I decided neither were worth the money for me as I did not find them accurate but many people find the Libre a life-changer.
I recommend reading this to get some initial information to work out what you want:
https://www.diabetes.co.uk/cgm/continuous-glucose-monitoring.html