Are these suitable for underfloor heating?
Yes, I can confirm that these trays are suitable with Underfloor heating.
They are based on good insulator - XPS - therefore your UFH should be installed on top of the tray, under the tiles. If it was installed under the tray, it would only have a very limited effect.
Please notice that there is a limited space from the shower tray surface to the upper grate edge. In case of this tray it is 20 mm you have to accomodate your underfloor heating, tile adhesive and tiles.
I am happy to assist if you have any questions.
David 020 7193 0953