If you don't user the "feet" that tray must be fitted using builders sand and cement mix otherwise it will crack further down the line. When I rebuilt my bathroom last year I used a shower tray similar to that and ordered a easi-plumb kit for it as there was no way I could get the waste through the floor to the stack. However, after seeing the easi-plumb kit I decided against using it and built a plinth to sit the tray on instead, that way I keep access to the plumbing. After watching a load of Youtube guides I fitted it with the sand/cement mix, levelled it and let it set and it's been perfect so far. I didn't use tiles though, I used Aquaboard around the shower instead. The rest of the bathroom has PVC bathroom cladding.