hi, Dragons have a hard time walking on smooth surfaces, so youll want something with texture to it. If you can find slate tiles they haave the added bonus of keeping ur beardies nails filed down too. I wouldnt go with a smooth glossy tile, itd be too hard to walk on...
To offer a different opinion: I am currently using natural slate. These tiles are really heavy and awkward to clean because they have tons of little crevices. Additionally, I have no way to cut them. I plan to redo the flooring for the bearded dragon and have textured vinyl tiles stuck to a sheet of plastic laid into the terrarium. That way I can easily clean it since it's vinyl and I can easily remove the entire flooring for deep cleaning since they are lightweight and all stuck to the sheet of plastic.
I am not really sure of the prices that site is listing for tiles. It's £24.44 for a 12"x12" tile? I paid $1.50 for a 12"x12" natural slate tile.