They are lightweight - unlike other bathtubs, fiberglass bathtubs and shower trays do not require the extra effort and expense of reinforcing the bathroom floor. They are also easy to unload and carry.
They are easy to repair - A cracked fiberglass bathtub and shower tray don't have to mean a replaced fiberglass bath tub. Often cracks can be repaired using a polyester resin repair kit.
They are low cost - Molded fiberglass bathtubs and shower trays are available at a variety of price points, comparing other steel or solid surface, fiberglass bathtubs are probably the cheapest option in the market.
They are bacteria-free
Their shape can be customized as per required design