I tried magnesium citrate for a while and I didn't see any difference
Often I get cramps in my legs after being active during the day. Normally taking a fizzy magnesium tablet immediately help to get rid of the cramps.
Some with type 2 diabetes can benefit from magnesium supplements. If you are deficient, then there are benefits. Those that have had high blood glucose numbers for years, might benefit from short term supplements.
There are several blood tests that each have their place in testing for magnesium. The blood serum test might give a more accurate view of if you need to supplement.
Many of us are deficient in multiple diferent vitamins and minerals. For me: ALA, chromium, berberine, CoQ10, B, C, D, help a little more. Then again, I have multiple additional health issues that put strains on my system.
Good luck.