These are just different methods of producing a seamless, waterproof floor. They are aesthetically very similar when first installed but after time the differences will become apparent.
A Solidity floor is made using 12mm thick Corian or HI-MACS so it is strong, crack resistant and very tolerant of structural movement. It therefore works well in houses with wooden floors as it can move with the building. The 12mm thickness means that if the floor is scratched or chipped it can be re-polished, or if damage is deep, a new section can be inserted discretely.
In comparison, an epoxy coated floor has a thin layer of epoxy resin which is less impact resistant and more brittle that Corian or HI-MACS. Most suppliers of resin or epoxy floors will only pour the resin and will not guarantee your floor staying crack free if there is a problem with the substrate.
Solidity's 15 year warranty covers the installation of both the substrate and the HI-MACS or Corian finish to give you peace of mind.
For more information about Solidity's wet flooring options take a look at wetrooms floors and bespoke shower trays.