Getting any benefit from potassium OTC supplements is like spitting in the ocean. We are supposed to get 4.5 grams a day from our food intake. Some foods are higher than others.
Cantaloupe has 1400mg or so in 1/2 melon.
A V8 has about 600mg.

An RX potassium supplement varies from 600mg to 800mg.
So 99mg tablet is nothing OTC. FDA limits higher numbers for OTC tablets. You'd have to take 6-8 tablets OTC to equal one V8 ( the low sodium one has more potassium than the regular).

www.nutritiondata.com gives mineral values for just about every food there is. When consulting this source watch the serving size...since some are unrealistic or misleading. Check what you typically eat and see how much of magnesium and potassium you typically consume.

But for magnesium 3 oz of unsalted almonds can give 270mg.

I don't think really high magnesium is needed. We are designed to eat a certain amount daily, and flooding your body with this is not natural. High magnesium intakes in people with impaired renal functions can lead to a build up in the body.

I have seen profound changes in people just taking 2 SlowMags a day! The RDA is about 400mg for an adult, elemental daily.

You can soak in magnesium...by making baths of epsom salts.
This lets some magnesium into the body where circulation may be impaired and so if mag has trouble getting to the toes and fingers.
Use lukewarm water, and about 4-6oz in a bathtub. When tiny blood vessels get clamped down, what you consume orally may not reach feet and hands. Once those vessels open up, nutrients can flow much better. (and toxins can be removed more efficiently). Magnesium baths are very relaxing to the muscles and can reduce pain too.

Remember when reading labels of magnesium products...some do not list contents in ELEMENTAL values. Some do. So a high dose of magnesium malate 1000mg, is really 150mg of magnesium elemental!

So if your cramping is confined to the feet do some soaks with epsom salts to get you relaxed and the blood flowing properly, then the oral can work better.