I'm very surprised he wasn't happy with a result of 47. I've always been told to aim for 48 or below as a general rule of thumb. Personally, I'd be very happy going from 53 to 47, As long as you aren't having too many hypos which is bringing that average down then I don't see any issues.
In terms of a ketone machine tester, I would agree with him in that regard, although you haven't felt unwell it is always good to have one on hand to test with just in case your blood sugar goes above 14 for any unexplained reason or if you have an infection, feeling/being sick but blood sugars are normal. Never quite know when ketones can sneak up on you.