Most of today's shower pans and bathtubs should be set in a bed of mortar to make them feel solid. Many will specify this in the installation instructions as a good option.
I know nothing about the shower you are looking at. There is a lot of flimsy junk on the market.
I recently installed a Sterling (Kohler) Ensemble 60" shower in a mortar bed and am very happy with it so far. It is the Vikrell material.