how much difference?
Those are for home use, and any of them could have a 10 point (mg/dL, )
difference between repeated measures even on the same glucometer.
Glucose concentrations changes fast and constantly in human body, so you do
not want to be overly enthusatic and try to get accurate readings. An
approximate range is good enough for most people.
Any brand should be good enough for this purpose unless there is something
wrong with the machine, the test strips or the usage.