Magnesium is important because it helps to calm muscles and nerves. Lack of Magnesium can lead to cramps and muscle seizures, including both the heart and brain, both potentially fatal. The trouble with most magnesium supplements is that unless they come in a certain form (slow-release magnesium chloride), they tend to go right through you (laxative effect), resulting in your bowels emptying with little or no benefit from the magnesium itself.
Where I live, I have found it virtually impossible to get hold of any slow-release Mag-Cl supplements and I have tried the more common Mag Oxides, etc. with little/no benefit except for empty bowels within 30 mins of digesting!
The alternative to supplements therefore are natural sources of magnesium, principally dark green vegetables. The darker the green, the higher the chlorophyll and hence also the higher the magnesium content. DO NOT boil but steam instead in order to retain all the goodness. Even better, consume raw if you can. TIP: try some raw florets of broccoli dipped in home made mayonnaise. Kale chips are also a delicious alternative.
The alternative to green veg is cooked meat juices i.e. save your cooked meat juices and pour them over your food before serving.
If you are experiencing regular muscle cramps then you probably have a magnesium deficiency. However, if you stick to these two simple suggestions then you should easily cover your magnesium requirements and stop the cramps, without having to buy any expensive supplements.