I assume your new meter tests both ketones and BG so you are planning to ditch your old meter.
In my experience my GP does not know one end of a BG (or ketone) meter from the other so will have no clue why you have changed.
In your position, I would just explain that my current (old) meter is not fit for purpose because it cannot test for ketones. Therefore you need BG test strips for your new meter. I would not put the idea into your GP's head that you could carry around both.
You do not explain why you are not happy with your old meter but you could explain this to your GP too.
One meter cannot fit all - we have different requirements for ketone testing, automatic dosage calculation (or not), poor eyesight needing a bigger screen (or not), ability to upload to Diasend for diabetes team to review (or not), ruggedness, ...