I have heard the same thing. If you do alternate site testing it is about 15 minutes behind a finger reading. So for a normal reading it wouldn't matter but if you think you are hypo, use your fingers.
According to Tyson Bio, Alternative site results differ from fingertip results when glucose levels are
changing rapidly such as after a meal, after taking insulin, during exercise,
or when you are ill or under stress. Use blood from a fingertip rather than an
alternative site if:
● you think your blood glucose is low,
● you don’t regularly have symptoms when your blood glucose is low, or
● how you feel doesn’t match the results from the alternative site.
● When you have just taken insulin, or any time during or after exercise.
● When there are unknown variables occurring in your day, such as illness.
● Whenever you are about to drive.