Gypsum, ever used it?

Espoma Garden Gypsum is the finest grade pelletized gypsum available. It is a natural, high purity mineral that provides valuable benefits to soils and plants. While Espoma Garden Gypsum is not a fertilizer, it can help increase the productivity of all your gardening efforts.

Benefits:

• Loosens clay soils and helps improve water and air penetration.
• Aids in minimizing salt damage to plants.
• Helps promote root growth and maximizes fertilizer effectiveness.
• Ecologically safe, nontoxic, nonburning; safe for plants, pets and people

how much to use would help i have 50 lb bag i discoverd in garage grandad always used it in garden but he's passed so cant ask him , need like 5 gallon pots how much how often