I never assume any of them are accurate - and comparison testing with the same drop of blood shows that up very clearly.
It must make calculating insulin doses very trying!
Luckily, I am T2, not on insulin, so all I need are the trends, and a rough guide of whether a meal sent me high, or whether it is time I ate again.
There are also other things that make the paying too much attention to the detail a hiding to nothing. Exactly the same meal can send a person up by different amounts on different days, depending on a whole host of different things - exercise, stress, tiredness, speed of digestion, alcohol, temperature... so it really is the trends that are important, not the detailed figures.