A BG meter is so much more useful than a one-off test. Because you can not only test your reactions to meals that you may be uncertain of, but you can also monitor your progress. The blood cells tested for glycation in an HbA1C test live for 3 months, so at best it is an average of you you did over the last 3 months with a slight recency skew.
If you are eating to your meter, then an HbA1C blood test more often than 6 months or even every year is pointless, because you will already know how well o9r badly you are doing rather than trying to correct things you mistakes you may have made months ago.