The primary purpose of security covers is to protect children and pets from falling in the pool, but they also keep debris out of the pool and require no maintenance during the winter months while the pool is closed. They anchor to the patio with brass lugs that screw flush with the patio when the cover is not in use. These covers are as strong as they claim as they can hold up to 500 pounds of weight.
The alternative to the security cover is a tarp style cover. It is the cheapest option but is not nearly as safe or secure because they are held in place with water bags. Rain or snow will fall on these covers over the winter months so they are not very nice to look at.
A typical tarp cover will cost a couple hundred dollars. A security cover will be between $2,200 and $3,000 installed. The tarp option is definitely cheaper, but most customers see the value in paying more for looks and security.