We all usually have magnesium deficiency, yet not all magnesium supplement forms are the same. Magnesium-citrate is the only form that has no influence on the digestive system (like constipation).
You may have heard that magnesium will help you alleviate headaches, because you need electrolytes. Also, you may have considered buying electrolyte powders (which are way too expensive for what they are). In such powders you will mostly find table-salt (which is dirt cheap), magnesium (you don't know in which form it comes) and potassium (which is abundant in many foods). These powders may also have some vitamins.
To be frank, they just make lots of money on nothing.. you can make your own mix of salt, THIS magnesium and some potassium supplement if you want to (potassium won't come in doses larger than 99mg due to regulatory stuff).
On a side note: Turns out this supplement helps a lot with sleep! Gave it to my mother to try, and she reported that she could sleep all night long (without me mentioning anything of this sort to her).
I think it's good to have a good amount of magnesium in your body, for proper function and not as "modern medicine" says - just enough to function well. That's to say, why have just enough to function if you can have as much as needed to function at full capacity. (DO NOT OVERDOSE! Because having too much of one vital substance will damage the intake of another - see "vitamin wheel" on your search engine)
This supplement comes in a large quantity that will last for 4 months (for a single person), the pills are on the large end, but not huge.
Overall, that's the best magnesium supplement I managed to find on iHerb to date.
