Hi @itsme12p,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Yes, the Bastion Mastic Powder Tile Adhesive would be suitable for tiling your shower.
You may have come across advice suggesting that mastic is not suitable for use in showers due to concerns about organic compounds. While that may have been true for older products, it's not the case with modern cement-based mastics. These do not contain the problematic organic compounds that were once an issue, making them perfectly safe and appropriate for use in wet areas like showers.
Let me know if you have any further questions.
Jacob
