A small glass tile in a solid color like this is a smart-looking option. Avoid clear glass tiles that might look fogged up if water gets trapped behind them.
It is up to the manufacturer of any glass tile to recommend the proper setting materials for installation. This is an industry guideline and promoted by the TCNA.
Tip: When working on a shower floor or steam shower project, avoid tile with a mesh backer on it. Most are not rated for submerged use and can be a risky option.