Chemar's is this:

I found topical application of magnesium to work quickly, and just as quickly it wears off with a slight rebound effect for me.

I find oral helps more for me...especially in the legs.
I don't know why either. I think there is individual variance like there is with everything medical.

The magnesium malate at Puritan's is good. I have bought that version. The malic acid is useful for muscles etc. Many fibromyalgia treatments include malic acid.

That high dose magnesium malate does loosen me up, which I don't care for. It does not have that effect for my son, who uses the Puritan version too. It might be that the hard large tablet does not dissolve well for me.
For example the Ionic Fizz works much better for me.
As well as the delayed version, SlowMag. (I use the generic form to save $$ of this). I am very sensitive to the laxative effects of magnesium so I have to go slowly etc. Others don't have that issue.