McP77

You'll have no problems with FastFlex's strength. As with all floors make sure you have a solid adhesive bed.

As a tip, if you do use fastflex make sure you wear gloves and work very clean. The stuff doesn't move when it's started to set. Keep your joints clean too. Unlike a cement based adhesive when you can get the grout rake in, the fastflex is more rubbery, so not easy to clean after.