For The Tile Guys
Well, solid shower pans are perfectly fine and this brand is no exception; however, leaks can happen in other areas whether or not the pan was solid or tiled, or mudded, or styrofoam. Don't know what part of the world you're in but IMO I'd worry more about leaks making my shower fail after 5 years than I would about the odd earthquake.
Waterproof showers have come of age; it is possible to have shower stalls made to last 40 years not because they used a solid pan, or mud or whatever but because the entire system (walls, floor, pan and drain) are one sealed (therefore waterproof) unit. And if an earthquake destroys your shower pan and causes a leaking shower, then you really have more to worry about...
See, it's not how solid you make it, how much concrete you put in but how waterproof it is. That's easy to achieve with about $1000-worth of waterproofing kit and some drywall. If you tie your solid pan into the waterproofing of the walls behind the tile, and if the drain is suitable, it won't leak. And if an earthquake selectively makes your shower leak rather than crack your foundation, then changing it is 2 days work. But if you don't have an earthquake of that magnitude, leaks are something you will live with everyday. Aside from health concerns from molds.
Make it "waterproof".